Agree very much with anon.
Assuming it isn't physical because you don't seem to be insinuating that it is solely that, it sounds to me as though she has some irrational mental hang-ups about intercourse itself. These could be caused by abuse so I do think it's really important to tread lightly, and her getting into contact with a GP could be a step towards improvement there. Even if it is not so linked to a past experience, it really does sound like something that she could talk to a pro about, someone who is equipped to listen and give the best advice directly to her. Not to say you aren't equipped, but I think you know what I mean by that. (: I should say, there are some people that just will not do piv sex, at all, it's not even inherently asexuality, they just hate it. I don't think she necessarily falls into that category, but it's something to think about.
When you say she has low sex drive, does that apply to all of the activity you've had with her? So she doesn't respond physically or emotionally, by being turned on, with oral etc? You say you just 'want to feel physically wanted', so does she never show affection physically at all? =/
It's a tricky situation - you are not at all wrong to want more from the relationship, sex is staple for many and it isn't shallow to desire it. However, this is clearly an instance where your girlfriend really, really needs your support. It might not seem that way because she is locking you out, in a way, however I think that if you were to leave her now after two years it could really hurt her self-esteem. That's not to say you should be responsible for that at all, but as someone who loves her that much it is of course something to care about. I don't think she is 'crazy' and really think if this is the only issue with the relationship, you should not give up too soon.