Estella explicitly says that she has "no heart" in chapter 29:
"You must know," said Estella, condescending to me as a brilliant and beautiful woman might, "that I have no heart—if that has anything to do with my memory."
Pip, of course, does not believe her, because he is still convinced that Miss Havisham has "destined" him for Estella and Estella for him. Later, in chapter 34, on a page subtitled "My Love Unintelligible to Estella," she says,
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?
Estella has been warning Pip from the very beginning of their relationship that she is cold and manipulative (while at the same time tempting him on, as she has been raised to do by Miss Havisham). Pip's refusal to accept reality is Dickens's sadly satiric take on "love is blind."
The ending of Great Expectations, in which the chastened and wiser Estella and Pip find happiness, has perhaps been justly criticized for sentimentality. It is probably much more likely that anyone programmed from childhood as Estella was will never change.