Who is Biddy and what role does she play in Pip's life?Great Expectations by Charles Dickens

As part of his motif of the hardships of orphans, along
with Pip, Biddy has also lost her parents and kept by Mr. Wopsle's great-aunt, who is
her grandmother.  But, like Mrs. Joe, Biddy's great aunt brings her "up by hand" and
uses her granddaughter to arrange the transactions in the little general shop that she
owns.  A bright, energetic girl, Biddy teaches Pip his letters and to read and to figure
while he attends the great-aunt's school. 

A sweet child
and unselfish child, Biddy, who displays a great concern for whatever Pip does, becomes
his confidante.  Not realizing that Biddy loves him, Pip tells her of his amorous
feelings for Estella, his hopes for the future.  When he leaves to go to London and
follow his "great expectations," Biddy asks Pip if she and Joe might walk a little
farther with him.  Pip kisses her, promising to tell her everything as they part. 
However, once Pip arrives in London and begins to put on the airs of a gentleman, he
forsakes the loving friend, Biddy.  

Soon, though, Biddy
becomes the housekeeper for Joe and Mrs. Joe, who has been attacked and is in poor
condition.  On behalf of Joe, Biddy writes to Pip, saying that Joe will visit him in
London. But, by this time Pip has become snobbish and he is anxious about Joe's
appearance and behavior before his gentlemen friends.  Of course, Joe senses this and
tells Pip he will visit him no more; he tells Pip that he must come to the forge where
he will always be welcome. 

After his sister's death, Pip
finally returns to the forge with much uneasiness and guilt.  He displaces his guilt by
being harsh with Biddy, telling her "I think you might have written to me about these
sad matters."  To this, Biddy perceptively and ironically replies, "Do you, Mr.
Pip?....I should have written if I had thought that."  As they converse, Biddy tells Pip
about his sister's demise and asks pointedly if he will come to see Joe, really.  Pip is
offended and scolds Biddy.  As he leaves, he has the boldness to tell Biddy that he is
not angry with her, but "I am hurt."  But, Biddy is right; Pip does not return to the
forge for a long time.

Clearly, Biddy, in her simple and
honest and humble manner, is a foil to Pip.  She is without guile.  Even when Pip
returns and is accusatory, Biddy speaks calmly to him.  As Pip finally returns home, the
prodigal son who begs forgiveness, he asks her to receive him as well.  The Pip is so
bold as to propose marriage to her, but Biddy does not offer any reprisals.  She simply
lets Pip days later discover that she and Joe have married.  Yet she remains ever the
friend to Pip, encouraging him to marry.  And, when she and Joe have a child, they name
the boy Pip.