Considering how repressed she is and how off put she was by the mere idea that Kaede would "be into that stuff" the obvious elephant in the room is when Kaede finally makes it clear that he wasn't just sexually assaulted, he was outright raped as in full on intercourse against his will.
That is what is going to trigger her and cause her to distance herself and reject him. She will see him as impure and tainted because he participated in the forbidden act and she won't care about the context because to her the context is irrelevant, the act itself is all that matters.
I don't completely agree with people saying she doesn't actually care about him and is only using him to fulfill her ideal romance fantasy. She didn't know about him being "pure" prior to becoming smitten at first sight, that was only a revelation that came about after the fact. It is just serendipity that his trauma aligns with her desires (to an extent). That said, their goals are clearly not similarly aligned as Kaede has expressed a desire to return to normalcy which most likely includes having a healthy sexual relationship (it wouldn't be overcoming trauma if he never has sex again, that would be letting his trauma dictate the rest of his life). She isn't being willfully ignorant so much as her delusions are giving her a bias towards seeing him in a particular light.