Who is Millie Tydings from Dicey's Song and what is their importance?

Millie Tydings owns a local store in the town where Dicey and her siblings have settled. Millie is a simple minded woman who struggles to run the store alone. Dicey convinces her to give her a job. Dicey helps Millie keep the store clean and to order supplies from her distributer. Millie knew Gram as a child and is a source of a great amount of information on Gram for Dicey.