I'm not a psychologist, but I listen to one on the radio. [come on I had to throw in a semi-Simpsons quote].
But seriousally, I've listened to Love-line so often that this sounds really familiar. Every single time I've heard "I don't have any memories of being abused" or "I don't think I was abused" the girl usually was. If there's uncertinty about the issue it, atleast from what I've observed, the person has been abused.
Don't the idea that she was possibally abused freak you out. I was physically, emotionally, and verbally abused when I was a child. It was fucked up, but you know... I don't think of it like that. I am who I am because of it and I've used my experiences to help others. I'm now involved in mentoring and Big Brothers, Big Sisters.
I say this not to stroke my ego, but to show you people that have been through shit are not damaged goods. Your GF is still the same person you've fallen in love with.
If you really wish to help her, back off the sex for a while. I know it's fucking hard, I dated a girl for 2 years w/o geting any at all because of her religious beliefs (which I respect). Encourage her to see a new psychologist if she feels her current one isn't helping (I would guess she's allready seeing one, right?).
Above all, don't push sex (unless there's times she's into this [in a safe enviorment of course
]) and don't make her feel like their's something wrong with her because her labido isn't up-to-par with yours.