One of the inevitabilities that I've found with a friends-with-benefits situation is that, at some point, one of you will develop feelings for the other and it just leads to awkwardness; the whole point of it is the casual, no-strings aspect. In this situation, the feelings are already established and even if she can turn them off and just see you as a sex object, you cannot do that yourself... she means more to you than that, I'm sure.

Yeah, you can carry this on and get your rocks off at the same time, but you'll feel worse for it. My advice would be to steer clear, because she needs to take you back on your own merits or move on, not use you as a means for getting off.

If she doesn't want you as a whole, she doesn't deserve to have you at all. :3