Estella is a very sad case. She never had a chance. Miss Havisham might have been a wealthy woman, but she was not mother material. She had recently suffered a huge emotional blow, being left at the altar, and she never recovered from it.
Miss Havisham carefully trained Estella to be cold and uncaring, and to lead men on and then break their hearts. Estella soon grew to feel that she had no heart, no emotions. In chapter 29, Estella tells Pip that she has no heart, "no softness there, no—sympathy—sentiment nonsense.” (enotes etext p. 162)
The fact that Estella says this, and is willing to tell Pip, means that she is already beginning to transform. She knows that she doesn’t feel, and she resents it. She wishes she had more gentle emotions.
In chapter 38, Estella reaches a catharsis. She argues with Miss Havisham, who berates her for being unfeeling.
“You should know,” said Estella. “I am what you have made me. Take all the praise, take all the blame; take all the success, take all the failure; in short, take me.” (p. 206)
Estella realizes that Miss Havisham has done this to her, and made her this cold, unfeeling person. She is angry and hurt.
“At least I was no party to the compact,” said Estella, “for if I could walk and speak, when it was made, it was as much as I could do. But what would you have? You have been very good to me, and I owe everything to you.” (p. 206)
Estella realizes that she was manipulated from a young age, and that she was raised to entrap men and break their hearts. She is angry because she wants to have normal feelings. This is where she begins to change. Pip comments that it was the first time he had ever seen them argue. Estella has had enough. Sometimes people have to reach their breaking point in order to change.
Estella does not change immediately. She continues to suffer, but in a self-punishing way. In chapter 45, when Pip tells her he loves her she calmly tells him she cannot love him back. She marries Bentley Drummle, who is loutish and abusive, instead.
"When you say you love me, I know what you mean, as a form of words; but nothing more. You address nothing in my breast, you touch nothing there. I don't care for what you say at all. I have tried to warn you of this; now, have I not?” (p. 244)
When Pip returns to Satis House much later, after his experiences with Magwitch and hers with Drummle, she seems completely different to him. She even comments that she is “greatly changed” (324). In conversation, we learn that she has lost everything except the land of Satis House, which holds mostly unhappy memories for her, but is still in her heart. Her beauty and her riches are gone, but she seems somewhat more content. For once, she has a heart.
[Suffering] has been stronger than all other teaching, and has taught me to understand what your heart used to be. I have been bent and broken, but—I hope—into a better shape. Be as considerate and good to me as you were, and tell me we are friends.” (325)
Pip and Estella will never be happy, but they agree to be friends. This is a big step for Estella. Estella has accepted her lot in life, and her new station, and now that she is free from Miss Havisham’s influence she can grow. Like Pip, she is satisfied in the end.