I can't tell if you're frustrated because you feel she doesn't want to be in a relationship or if you're frustrated because you can't be in a relationship where this sort of thing goes on.
I'm a sufferer, and I typically do not isolate from my partner, although I isolate from nearly anyone else. If I were in a relationship with someone who has PTSD, and they isolated for weeks from me, I would not be able to tolerate it, and I'd tell them I was finished.
I require a lot of attention daily from my partner, and the only circumstance under which I seem to be able to tolerate not getting it is mitigating circumstances such as travel, work, or family crisis. That's just who I am and what I need.
ETA: I'm not saying this may not be very normal behavior from her and related to her PTSD. I'm saying that I would not be willing to tolerate that behavior personally. I'm just challenging you to identify your own needs, boundaries, and limits.