Allie Nelson is a student at South Park Elementary. She often appears as a background character, who has been seen in Mr. Garrison's class. She took Pip Pirrip's seat in the classroom after he died, as seen in "Royal Pudding".
She has shoulder-length brown hair. She wears a purple sweater and a grey skirt. She also wears black shoes and can usually be seen holding a teal trapper keeper.
She is quite notable for being one of the few girls at school who is always seen wearing a skirt, other than Girl with Blonde Hair, Henrietta Biggle, Kelly P. Gardner, Monica Ryland, Sally Darson, Shauna, Sophie Gray, and Theresa.
- "The List"
- "Tonsil Trouble"
- "Super Fun Time" - Seen as Theresa's partner during the field trip.
- "Elementary School Musical"
- "The Ring" - Seen at the Jonas Brothers concert.
- "Butters' Bottom Bitch" - Seen in the classroom.
- "The Tale of Scrotie McBoogerballs"
- "Coon vs. Coon & Friends" - Seen at the Justin Bieber concert.
- "Royal Pudding"
- "Bass to Mouth"
- "Jewpacabra" - Seen at the Easter egg hunt.
- "Butterballs" - Seen in Stan's anti-bullying video.
- "Cartman Finds Love" - Seen in the background in Mr. Garrison's classroom.
- "Sarcastaball" - Seen in the background in the school hallways.
- "A Scause For Applause" - Seen in the background in the school hallways.
- "Gluten Free Ebola" - Seen at the party.
- "Grounded Vindaloop"
- "Stunning and Brave"
- "Where My Country Gone?"- Seen on the playground.
- "The City Part of Town"- Seen in the hallway.
- "You're Not Yelping" - Seen in the school hallway.
- "Safe Space" - Seen in the school hallway.
- "The Damned"- Seen in the hallway.
- "Wieners Out" - Seen in the stands at the volleyball game.
- "Douche and a Danish" - Seen in the battle between the girls and the boys.
- "Hummels & Heroin" - Rallies with Marcus Preston after witnessing his presentation in the school cafeteria.
- "Sons A Witches" - Seen at the pumpkin patch.
- "Moss Piglets" - Seen in the school hallway.
- "SUPER HARD PCness" - Seen in the hallway evacuating to the gym.
- "Dead Kids" - Seen in class.
- "A Boy And A Priest" - Seen at Clyde's party.
- "Tegridy Farms" - Seen in the corridor and in the lunch room.
- "The Scoots" - Seen in the cafeteria. Later trick or treats.
- "Time To Get Cereal" - Seen in the school's playground after evacuation.
- "Buddha Box" - Seen in the classroom.
- "Band in China" - Seen in the corridor.
- "Let Them Eat Goo" - Seen in the classroom and in the cafeteria.
- "Board Girls" - Seen at the school assembly and at the Board Girls Gaming Club.
- "Basic Cable" - Seen on the playground.
- "The Pandemic Special" - Seen in quarantine at school with the other students.
Rumors were spread that Allie Nelson visited the Unplanned Parenthood Clinic, accusing her for being a whore. She was later cleared of her name.