By the time that Pointer steals Hulga's leg and glasses, I think Hulga has lost all illusions of actually taking anything from Pointer. By that point, Hulga has begun to realize exactly how deeply she has misjudged this Bible salesman. I believe that this question is asking about Hulga's thoughts the night before their rendezvous. Hulga imagines herself seducing Pointer and him being extremely remorseful about it because of how it violated his Christian faith. A reader might conclude that Hulga is hoping to steal his innocence, but Hulga also then imagines that she would take/steal Pointer's supposed remorse and change "it into a deeper understanding of life." I think Hulga is planning on stealing Pointer's faith and worldview. She doesn't want to take it for her own. Rather, she wants to take it from him, so he can become more "wise" and cynical like her about the world.

During the night she had imagined that she seduced him. She imagined that the two of them walked on the place until they came to the storage barn beyond the two back fields and there, she imagined, that things came to such a pass that she very easily seduced him and that then, of course, she had to reckon with his remorse. True genius can get an idea across even to an inferior mind. She imagined that she took his remorse in hand and changed it into a deeper understanding of life. She took all his shame away and turned it into something useful.

Hulga hopes to use Manley Pointer for immoral purposes.  She believes that he is a very spiritual person, he is a Bible salesman.  She thinks that she can shock him with her willingness to have casual sex with a man she just met.  What she doesn't realize is that Manley Pointer is more cynical about life than she is.

While Hulga arranges to have a secret rendezvoux with Pointer, he has secretly become attracted to her because of her wooden leg.  So they are actually setting each other up for selfish purposes.  What Hulga does not realize is that she is not as heartless, cold and lacking in faith as she thinks.  She is confronted by a sadistic, manipulator with an oddball fetish, Manley Pointer, collector of prosthetic devices, conned from innocent women who swooned for his attention.