Mike J has a point, sex is not just a physical act but an emotional one as well.. the emotions involved could very easily be what is triggering her.

As for the relationship, it doesn't sound very healthy, somebody shouldn't give their partner a time limit on getting better and the phrase that bugs me is "get better for him" if he was really invested in her emotional well being he would want her to work on it or "get better" for her own emotional well being not his own satsifaction....and he should be picking up on her body language and hesitations, espically if he knows her apprehensions and fear concering sex and sexual acts...

As for what you can do, that is a tricky situation, offer your opinon and information on the subject, you cant' make choices for her, I know it's hard when a friend is in a situation and you can't do anything to help, but you aren't responsible for her actions, and nobody can be helped unless they wish to be, just be her support and if your okay with it maybe you could show her this thread with the repsonses? I understand if the last one is a no, but it was just a thought.

I hope things get better for your friend and you

Best Wishes
Typo