In chapter 29 of Great Expectations, does Estella really have "no heart, no softness, no sentiment"?
Yes this is true. Dickens created her character to never have any capacity for tenderness or human emotion. As the conversation continues after the line you recorded in the question, Estella goes on to tell Pip that she has never had feelings for anyone and if the two of them were ever to be in a relationship, she would continue to have no affection for him. Readers are led to believe that this line of thinking comes from the bitter Miss Havisham who has trained Estella from a young age to hate men. Part of this comes from Havisham's skewed idea of love:
"I'll tell you ... what real love is. It is blind devotion, unquestioning self-humiliation, utter submission, trust and belief against yourself and the whole world, giving up your whole heart and soul to the smiter - as I did!"
Everyone defines love differently, but I am confident that many people would agree that true love would not require all of these sacrifices. Surely there is some sacrifice in love, but a companion in such a relationship would likewise make sacrifices. Readers believe that Havisham's experiences have affected how she trained Estella to live. It seems Havisham has worked the soul and capacity for human care right out of Estella. Estella's character remains true to these characteristics until the end of the story.