Who is Sybil Ann Dorsett from Sybil and what is their importance?

Sybil Ann Dorsett is pale and extremely thin. She has ash-blonde hair and gray eyes. She is described as listless, and Dr. Wilbur diagnosis her with neurasthenia. Sybil Ann only assumes control when things become overwhelming, but she has to concentrate on moving the body or she will just stop moving. As she sits on Dr. Wilbur's couch, Sybil Ann appears to grow visibly smaller. She is similar to Hattie Dorsett during her catatonic period at the farm.