In Great Expectations, why does Miss Havisham agree to help Herbert?
To answer this question you need to understand how Miss Havisham at this stage of the novel mirrors the development in Pip's character. It is in Chapter 49 that Miss Havisham decides to help Herbert, and it is also this chapter that features her dramatic repentance and likewise her even-more dramatic burning.
It is in Chapter 44 where Pip first asks for Miss Havisham's help in supporting his friend Herbert and it is interesting to note that he talks then to a very different Miss Havisham who is unrepentant and freely admits that she used Pip to torment her relatives. She also declares that she never encouraged Pip's idea that his benefactor was her, by stating: "You made your own snares. I never made them." However, as readers we are suspicious of such claims, as Miss Havisham at various stages has used and abused Pip in ways that suggest she had some claim over him.
Yet in Chapter 49 we have a very different Miss Havisham. Her own increasing realisation of who she is and what she has done mirrors Pip's own greater sense of self-understanding, and also allows him to show forgiveness as he now knows that he needs forgiveness himself. Her repentance is symbolised in her willingness to help Herbert and also to help Pip and shows a reversal of her self-imposed exile from life and her family.