Biddy was Mr. Wopsle's great aunt's granddaughter. She was an orphan like Pip. Physically,Pip says of her,
"Her hair always wanted washing, her hands always wanted washing, and her shoes always wanted mending and pulling up at the heel." (pg 40 - chapter 7)
However, Pip explains that this was her weekday attire. She always went to church on Sunday dressed up.
She was kind and patient. She helped Pip with his reading because Mrs. Wopsle always fell asleep during class. She took care of Pip's sister when she was attacked. When Pip goes into debt and falls ill, Biddy convinces Joe to go to him.
She is a good friend to Pip. He tells her about Estella, and Pip swears her to secrecy when he gets his chance to become a gentleman. He asks her not to tell where his fortune originated. Of course, at this time, he thinks his benefactor is Miss Havisham. Biddy tells Pip,
"I am glad of one thing, and that is that you felt you could give me your confidence, Pip. And I am glad of another thing., and that is that of course you know you may depend upon my keeping it." (pg 121, chapter 17)
When Pip compares Biddy to Estella he says,
"Biddy was never insulting, or capricious, or Biddy today and somebody else tomorrow; she would have derived only pain , and no pleasure from giving me pain; she would rather have wounded her own breast than mine. How could it be then, that I did not like her much the better of the two?" (pg 122- chapter 17)
Biddy was intelligent. She could keep up with Pip's reading and "learn everything that I learn" Pip says,
"You are one of those, Biddy, who makes the most of every chance . You never had a chance before you came here, and see how improved you are." (pg 118)
After Pip's sister dies, she opens a school and becomes the school mistress for the town.
Biddy is responsible and organized. She takes over the household with Pip's sister is attacked.
Pip asks Biddy to educate Joe "in his learning and manners" so that he wouldn't be so backward and he will be ready when Pip comes back a gentleman. But she is a good judge of character too. She tells Pip that Joe,
"....may be too proud to let anyone take him out of a place that he is competent to fill, and fills well and with respect. To tell you the truth, I think he is -- though it sounds bold of me to say so, for you must know him far better than I do." ( pg 139 -chapter 19)
However, she does teach Joe to write, and he does take pride in it. Later, in the novel, she marries Joe, and she truely loves him. Pip says,
"There was something in the action and in the light pressure of Biddy's wedding ring that had a very pretty eloquence in it." (pg 448- chapter 59)
Biddy is a direct contrast to Estella. She is everything Estella isn't due to Estella's upbring by Miss Havisham.
I have given you the page numbers and chapters since my edition of the book may differ from yours.