Originally from New York City, New York, her parents divorced and her dad moved her out to the mountain town of South Park, Colorado. She initially had complained about this ordeal, because she missed being near Broadway with all its musicals and plays. Soon after moving, she quickly forgot about her complaints and was eager to meet new people. She was the new kid to Mr. Garrison's fourth grade class and easily made friends with Wendy and the girls.

Growing up around Broadway, Percy fell in love with theatre, and begged her parents to get her voice and acting lessons. At first she had to quit taking lessons when her and her dad moved, but he was able to get her instructors to do zoom lessons with her. She dreams of becoming a Broadway star and her dream role is Maureen in RENT (her favourite musical).

Percy can be seen walking around Stark's Pond with her book on butterflies. She's hoping she can spot some that she's never seen before. If she comes across an injured butterfly she tries her best to nurse it back to health. If she's too late, and it has already died, she'll add it to her butterfly collection in her room.

She can mostly be seen hanging around Butters/Marjorine and Tweek, however she does like to follow the goths around even if they tell her to get lost. This is because she has a massive crush on Pete Thelman.