She has been Milo's close friend for a very long time. As the only person brave enough to choose to face Murphy's Law on a daily basis, she remained one of Milo's only friends until they met Zack. While as of yet we have no confirmation, it is very likely that the two met at a very young age, as evidenced by her having photographs of Milo from when he was little ("Missing Milo"). Over the years, Melissa dedicated a lot of her time to collecting vast amounts of stuff from Milo in an attempt to cure Murphy's Law. Eventually, she realized he wouldn't want that, but she kept collecting information anyway, for reasons she herself is unsure of ("Missing Milo").Her two front teeth are fake- at one point in her life, she'd lost her real front teeth after catching a pop-fly to the face ("Secrets and Pies").
On the first day of summer before the current events of Season 1, Melissa had been setting up a science project when a helicopter dropped a roller coaster into her backyard, crushing the project. This caused her to develop a crippling fear of roller coasters that she tried to keep hidden from her friends until they helped her get over it at Lard World ("Murphy's Lard").
Being Milo's friend, Melissa has gone on many adventures with her best friend, E.g putting away robots in a shark cage and going to a lumber yard to apologize ("Missing Milo"). One of her and Milo's most famous adventures was "The Llama Incident". A trip to a llama production of Hamlet went horribly wrong, leading to Melissa and Milo chasing after Milo's back pack from one crazy location to the next. The two manage to go through it and go on to look back at the adventure positively. They continue to treasure and laugh about it to this day ("The Llama Incident").
When Milo and Zack met for the first time, she took the bus so that she could help them get lunches. She made a wager with other students, betting that Milo and Zack would arrive at school on time. She won with seconds to spare giving everyone's lunches to the two. ("Going the Extra Milo")
She, Zack, and Milo teamed up for a science experiment for school. Determined and a little worried for her grade point average, She got to work. Her friends helped her much as they could and they made great progress. Despite some setbacks and close calls, the project was a success, even after a truck hit their project and it bounced all over town. They got an 'A' for the project in the end. ("Sunny Side Up")
She and Milo attended Zack's first football game at Jefferson County Middle School. They usually didn't due to Murphy's Law, but were allowed to because the game was "unwinnable". Though the two at least enjoyed each others company, the Geckos were losing badly. She jokingly suggested that Milo root for the other team, so that the Geckos could win. He jokingly did, which caused the Geckos to score. Coming up with a plan, she then told him to continue to root for the Tigers, leading to the Geckos winning the game. She then went with Milo to the hospital after he broke his thumb to support him. ("Rooting for the Enemy")
She, Zack, and Milo were separated from their class on the way to the natural history museum when their subway car disconnected and they wound up underground. They ran into a group of lost construction workers and took them to the surface at the natural history museum. While being in underground, she and Milo got buried alive by a bunch of rocks, and Zack was able to get them out safely. ("The Undergrounders")
She and Zack joined the Murphy siblings to watch the new Doctor Zone movie. They met two fans of the franchise who mocked them for being newcomers. She theorized that Doctor Zone and Time Ape are brothers, which angered the veteran fans. After Sara calmed them down and a pistachio cart took out the theater wall, the four watched the movie and her theory was proven correct, leading to the fans in the cinema to cheer for her. ("The Doctor Zone Files")
She and Zack helped Milo chase down a doctor's note needed to excuse Milo's absences. Melissa eventually became the anchor of the party by giving a number of motivational speeches when her companions were ready to give up. In the end, after nearly getting incinerated in a paper recycling center, she, Milo and Zack find the note and go to School. ("The Note")
She and her class visited their parents at their jobs and experienced Murphy's Law. The group first went to the water treatment plant to visit Milo's dad and experience a flash flood when the pipes broke. They then went to the Fish Hatchery to visit Melissa's father, where Milo starts a fire with water. Lastly, they visit Zack's mom at the Hospital where an MRI became a super-magnet. ("Worked Day")
She, Zack, Milo, and Sara spent a day at the Nowhere Desert Dude Ranch. After Sara went in search of a possible filming location for Doctor Zone, she and her friends ran into Jackie, a danger-seeking girl who enjoyed Murphy's Law. After surviving an avalanche, a raging bull, and a flash flood, they were picked up by Milo's parents, but they made a U-turn to pick up Sara. ("The Wilder West")
She, Zack and Milo went to Lard World, where Melissa revealed her fear of roller-coasters. She was convinced to ride one, but she panicked when she realized that Milo was on board. Zack managed to get off before the ride started. She and Milo rode the roller coaster twice. She eventually learned to cope with her fear of rollercoasters. ("Murphy's Lard")
Once when she and Zack visited Milo's house, the macaroni and cheese he prepared for them exploded, and they ordered pizza instead. She was shocked when Zack quickly shut the laptop as their delivery person started to sing. She revealed to her friends that her two front teeth are fake. As Veronica went to deliver their pizza, she and Milo discovered The Lumberzacks' song "Chop Away at My Heart", much to Zack's embarrassment. ("Secrets and Pies")
She, Zack, Milo, Mort, and Chad competed in a combined scholastic and athletic event, having just heard about it, against the Middletown Middle School Middlemen, who had known about it for three months. They did poorly until Murphy's Law kicked in. Jefferson County Middle School won the event. ("Athledecamathalon")
She, Zack, and Milo attended a school dance. She and Zack worked the coat check, and they and Chad defended Mr. Drako from what he thought were vampire hunters, though Melissa remained skeptical. They confronted the pair, and they left. They bumped into their teacher with a brief apology, and she was annoyed by Chad. She, Zack, Milo, and Mort filled in when the band mysteriously vanished. ("School Dance")
She, Zack, Milo, and Mort formed their own band and competed in a music contest. After Zack got frustrated after meeting up with his old band, she and the others grew concerned for him. After he snapped out of it, the four played for fun, enjoying themselves. ("Battle of the Bands")
Melissa, Zack, and Milo headed back to school after hours to get her math book. After they locked the only key in the classroom, the three went on a "quest" to find Fred, the janitor. They eventually re-entered the classroom and retrieved the key. She and Milo also met Fred. ("The Math Book")
She and Milo went with her father to drop off an antique fire engine at the Fire Engine Museum. Along the way, the truck's brakes gave out, and it went out of control. They finally stopped after crashing through the Natural History Museum and into the Tyrannosaurus display. ("The Little Engine That Couldn't")
After Milo mysteriously vanished, she and Zack went looking for him. They found his backpack. Two agents chased after them, but Scott delivered them. They returned to Milo's house and saw him in the 1965 pilot of Doctor Zone. She took Zack and Sara to her house to see her room dedicated to Murphy's Law. They saw two figures in most of the photographs. Sara took them to the home of Orton Mahlson, the creator, and star of Doctor Zone, to see if he knew anything. He gave them a letter from Milo telling them to go to Jefferson County Middle School at 3:00 PM. They arrived, only to find King Pistachion and his followers. Milo arrived shortly thereafter with Cavendish and Dakota, and the six took on the Pistachions until they were captured. They were saved when Diogee peed on the king's present-day self, killing the plant and stopping his kind from existing. ("Missing Milo")
She, Zack and Milo went to V-Tech to see Victor Verliezer, the CEO, present his new invention, C.I.D.D. When they learned that C.I.D.D. was not his, they set out to find his real creator. She found the creator, Clyde Rickenbacker, at a lumberjack festival when he posted a selfie with them in the background. They reunited creator and robot, but all were chased by Verliezer's security team. They live-streamed him mocking his customers, and he went out of business. ("A Clockwork Origin")
Once, she, Zack and Milo went camping. After Milo went sleep-walking through the woods, she and Zack chased after him, dealing with the effects of Murphy's Law. When Milo thinks they stopped him from wandering too far from camp, she hits him with his backpack. ("Perchance to Sleepwalk")
Her class took a trip on the school yacht. After Coach Mitchell battled a pelican, the yacht ran aground on an island, and all the faculty aboard, except Mr. Drako, went feral. The students fixed the ship and scouted out the island for fresh water sources. After they learned a tidal wave is coming that could take them home, they brought the feral faculty back to the ship just in time and made it home. ("Some Like it Yacht")
She and her father attended back-to-school night with Zack and his mother and Milo and his father. After their parents and Ms. Murawski are turned into toddlers, they chase them around the school and protect them from Murphy's Law. After they are returned to their normal ages, their parents look at them, and reminisce on when they were younger. ("Backward to School Night")
She scolded Elliot for insulting Milo. In the timeline where Milo was never born, Elliot inadvertently introduced her to Zack when asking about Milo. ("World Without Milo")
She and Zack helped Milo with Murphy's Law during a race and built him a makeshift finish line when the actual one was carried away. ("The Race")
She and Zack went skiing with Milo and his dad. They blasted into town on a high-speed toboggan. After the group crashed into a comic shop where Sara and Neal were, the shop's boiler lodges onto the toboggan, and they took off. When it stopped, she and her friends left the older teenagers alone. ("Love Toboggan")
She, Zack and Milo set out to see Hamosaur II and were entangled in Milo's shoelaces along the way. Milo's quick thinking saved them. ("The Island of Lost Dakotas")
She, Zack and Milo were saved by Cavendish and Dakota from falling out of the sky. After Milo and the time travellers headed to 1965, she and Zack were abducted by Derek's forces and imprisoned at Lard World.
One Halloween, she, Zack and Sara checked out a haunted house which Milo built inside a decommissioned truck. When Zack got separated from the girls, they continued through it and, unknown to her and Sara, the truck started to move. They did not notice until they got out and found that they were at Jefferson County Middle School. She and the Murphy siblings were scared by an exhausted and weathered Elliot arriving at the school. ("Milo Murphy's Halloween Scream-A-Torium!")
She, Zack, Milo and picked up the extended Murphy family for Christmas to surprise the Murphy parents. Along the way, they were stranded on the side of the road. They took a horse and carriage until it was stuck in a tree. They made their way to the mall and found the Murphy parents. They then decided to have dinner at the mall's Chinese restaurant, where they were joined by Zack's parents, her father, Mort and Amanda. (“"A Christmas Peril"”)
In "The Phineas and Ferb Effect", she and Zack are still prisoners of the Pistadhions, they meet Buford Van Stomm and Baljeet Tjinder and they form an escape plan with Zack, Sara, Buford and Baljeet distracting the guards by singing Chop Away at my Heart while she uses Murphy’s Law via Martin to escape. She, Zack, Buford and Baljeet escape while the rest are recaptured. They eventually run into Derek and later Candace Flynn. As the five are cornered they are saved by Phineas Flynn and Ferb Fletcher and meet up with Milo.
They go to Phineas and Ferb’s hideout to formulate a plan. When she and Zack see Candace take Milo somewhere, they follow thinking she is a Pistachion. After the four return and perform tests to see if they could weaponize Murphy's Law and build the Murphy's Law Suit before being captured by the Pistachions. They are taken to Lard World and she and the others except Milo, Phineas, Ferb, and the recently returned Cavendish, Dakota, Doofensmirtz, Orton and Dakota Paradoxes are turned into pistachion minions. After Derek is defeated in 1955 she and the others, except Bradley’s right arm, are returned to normal.
In "Snow Way Out", she make a wager with Bradley weither Milo and Zack get to class on time with the loser shoveling the winner’s driveway. As the bus gets closer to school she starts to doubt Milo. When they miss the bell Bradley proudly hands her a shovel and she ponders in disbelief, however this is under when Zack and Milo use Cavendish and Dakota’s time machine and she now hands a stocked Bradley a shovel.
In "Teacher Feature", she and Zack help Milo with a chemistry safety demonstration. However Murphy's Law causes Ms. Murawski’s desk to fall through a crack in the floor and their teacher to go after it. After their teacher and her desk are saved by Scott they two arrange a dinner date for the following night and she, Zack and Milo spend the day coaching Scott on how to behave and shadow him to enshure he behaves. In the end their teacher and Scott decide to remain friends.
In "Picture Day", she and Zack spend the day trying to help Milo get a good school picture. When they think they succeed whe they get a good picture, it inadvertently gets replaced by one of the Yeti.
In "Agee Ientee Diogee", she and Milo are seen in a flashback getting ice cream. She also says that she is "Murphy-ed out"
In "Game Night", she, Diogee, Milo and Zack decide to finally finish a board game. They are later joined by Sara, Neal, Cavendish, Dakota, and Milo’s parents. When the original game is lost they make a makeshift game out of other games. As they are about to finish a deadly vortex opens up over the house, and as the ten are sucked in they finish the game.
In "Pace Makes Waste", he and her friends go to a charity race for homeless llamas. When Elliot shows up she says Milo has more of a right to be there since his mother organized the event. When Milo and Elliot go on a “warmup lap” around Danville, she taps into various cameras so the race can be seen.
In "Lady Krillers", when Tobias Trollhammer in forms them of his fears of being fired or ruined due to a female lead in the next Krillhunter movie, she is excited at the female lead reboot but symphesises with the actor’s fears.. In response she, Zack and Milo dress Tobias as a woman to audition for the lead in the movie. Everything goes smoothly until Tobias loses his wig. She and her friends watch as he gives a brief speech saying he is the franchise. She and the others have mixed feelings when he is cast as the movie‘s villain.
In "Doof's Day Out", she goes with her class to the Natural History Museum to see the digestive system exhibit. When Zack’s claustroavoidence acts up, she and Milo help Doofenshmirtz build a go cart out of display organs and drive out before crashing into the gift shop.
In "The Ticking Clock", she learns that the clock her great-grandmother built has stopped and was sold to someone, Victor Verliezer, who plans to tear it down. She is helped by Zack, Milo, Clyde Rickenbacker and C.I.D.D. in repairing it. They spend the day fixing it to no success until she has Doof’s deguminator turn the gears, which had gum glued onto them, until they turn. They get the clock working and save it.
In "Managing Murphy's Law", she and the other members of Just Getting Started are drafted by Amanda to perform in the Forget the Llamas, Save the Alpacas benefit concert. While they rehearse they decide to change their name until they decide against it.
In "Milo's Shadow", she and her friends are shadowed by Doofenshmirtz for a day to learn how Milo copes with Murphy’s Law. They are annoyed by his inability to think things through.
In "Sick Day", she and Zack bring Milo his homework while he is home sick.
In "Field of Screams", she and Milo spent the day helping zack on his uncle‘s farm. Things go smootly despite Murphy’s Law and they get the chores done.
In "Spy Little Sister!", her father sighed her up for a woman-girl mentorship program, however she inadvertently gets sucked into a mission with Savannah to stop a robot from destroying Danville. They both use what they know to stop the robot and Savannah thanks her for her help before leaving.