Muffy, along with Loca, was part of Alana's posse. She would usually repeat what Alana said differently and would try and fail to translate Alana's Spanish. Her role remained unchanged when Bianca took over the group. She had a younger sister named Buffy who is just as much of a brat as she is.
Muffy's role was nothing more than repeating Alana's words comically at her Halloween party, and did the same when Alana vied for the affection of Devon Carter. Muffy was with Alana and Loca when they joined Raven's protest against Principal Lawler's decision to require all students to wear School Uniforms.
During Raven's sleepover, Raven told her and the others that she was psychic, but they thought it was part of her practical joke when it really was not.
In the episode "Sister Act", it is revealed Muffy has a little sister named Buffy.