When Biddy comes to the Gargery's, she makes a profoundly positive impact on everyone there: Mrs. Joe, Joe, and Pip. In Chapter 18, Joe is devasted by "the wreck of his wife." He takes care of the profoundly injured woman but it takes a great toll on him emotionally. When Biddy arrives to take over the duty, Joe is able to enjoy his life and even visit his friends at the Jolly Bargemen.
Biddy's healing influence is immediately evident on Mrs. Joe as well:
"Biddy instantly taking the cleverest charge of her as though she had studied her from infancy. Joe became able in some sort to appreciate the greater quiet o fhis life" (Chapter 18).
Biddy becomes so well-acquainted with Mrs. Joe's cryptic communication style that she is able to solve an important mystery: what the "t" represented on Mrs. Joe's slate--the woman's baffling desire to have Orlick visit her.
Pip also enjoys the comfort of Biddy's presence. He remarks that Biddy is "Pleasant and wholesome and sweet-tempered", and that he "began to think her rather an extradoinary girl." Biddy keeps up with Pip in his studies, and seems to know everything that Pip knows. Later, she gives Pip sound advice about Estella, and lets him literally cry on her shoulder. Despite Pip's bouts of self-pity and vanity, she is a steady, wise, forgiving presence, long after Pip has turned to new adventures.