Who is Peggy Lou Baldwin from Sybil and what is their importance?

Peggy Lou Baldwin is Sybil's anger. Whenever Sybil is under stress, Peggy Lou takes control of her body. Peggy is described as having straight black, bright blue eyes, a pug nose, and a mischievous smile. Peggy Lou seems to be the one who has born the better part of of Hattie's abuse of Sybil.