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

Marjorie Dorsett is a small willowy brunette. She is serene, but she is also quite vivacious. Marjorie is a party-goer and a tease. She refers to Sybil as "you know who", never using her proper name. Marjorie seems unaffected by Willow Corners, and the torture Sybil was subjected to.