Why do you think Miss Havisham manipulates and misleads Pip into thinking she is his secret benefactor? What, if anything, does she derive from this?

Miss Havisham does not originally set out to convince Pip that she is his benefactor. Her goal was to make Pip fall in love with Estella so that Estella could break his heart. When Pip began thinking that Miss Havisham was his benefactor, he kept it to himself for a while because that was one condition of his situation. However, as Miss Havisham picked up on Pip's assumption and chose to not correct him. She does derive a certain amount of joy from the suffering of others. Miss Havisham is carrying the scars of being mislead herself and abandoned at the altar. This event made her very evil and cynical, and she has made it her life's goal to see men humiliated and abused. Pip is able to make her feel a bit of remorse when he confronts her, but the damage is already done.