Who is Miss Havisham from Thursday Next in Lost in a Good Book: A Novel and what is their importance?

Miss Havisham is a character from Charles Dickens' Great Expectations. She lives in Jurisfiction, and her main purpose is to assist Thursday, who was recommended by Mrs. Nakajima, travel through books. In the end, Miss Havisham agrees to help Thursday hide in Jurisfiction until after the birth of her baby.