Who is Mary Lucinda Saunders Dorsett from Sybil and what is their importance?

Mary Lucinda Saunders Dorsett is responsible for keeping the household. She is described as a motherly type with a wistful tone. Mary wishes she could get out more, experience new things, meet people, and wear nicer clothes. She understands, however, that these things won't happen, and she does not voice her discontent like some of the others. Mary emerged after Grandmother Dorsett's death.