Bianca is the leader girl of Alana's former posse. She only appears in 2 episodes.
Ever since Alana got kicked out of Bayside, Bianca took over her role as the mean girl. As Muffy put it, Bianca was "so bad, she got kicked out of military school". Ever since she started going to Bayside, she immediately began to tormet Raven and her friends and family (even going so far as to follow her home and hit her dad with dodgeballs).
One day, during gym, Raven accidentally hits Bianca in the face with a dodgeball (which literally "knocked the bad out of her", as Chelsea put it). She turns good for a week, but because of that event, her former posse, Muffy and Loca, target Raven as their new leader.
She returned to her old self in the end of the episode after Raven falls on her from a rope.