Molly, Mr. Jaggers's housekeeper, is a minor character with a big secret: she is Magwitch's wife and Estella's mother. Molly had been accused of murder, but Jaggers was able to get her acquitted, and Molly became his housekeeper. Her daughter, Estella, rumored to have been also murdered by Molly as an act of revenge, actually is placed by Jaggers in the care of Miss Haversham.
Molly is an interesting character in that so much of the mystery surrounding Pip and Estella lies in her backstory. But more to the point, her "taming" by Jaggers (Wimmick calls her "a wild beast tamed") is an example of the power the lawyer has over the lives of the characters in this story. Molly is a passionate, virile woman who nevertheless is made subservient to Jaggers's calculations. It's an open question how much of Estella's character can be traced to Molly, or to Mr. Jaggers's management.