Hello, I happened by your post from a couple of months ago, not sure if you are still dating the same girl or not. Well, I have PTSD too (and I'm in my late 30's)from being attacked (in that way), car accident injuries caused by another person, and surviving physical abuse growing up from family. While everyone is different in their 'style' of handling the anxiety, memories, and triggers...usually it falls within a spectrum of behaviors and needs, at least for women. I would say first off, it's nice that you care at all to try. Second, try asking her directly "Sweetie, I want to help you feel happy, comfortable, and safe with me. Please tell me whatever I can do to help that happen?" Third, when someone's PTSD is 'triggered', the best thing to do is make sure they can 'escape' (if not at home), and also to say reassuring things like "I care about you", "everything will be okay baby", and "you are safe, I won't ever let anything happen to you honey" sorts of comments. If she is not 'afraid' but rather, 'angry' (tougher to calm down)...just understand that it's like having the same level of intensity/emotion you might feel as you would defend your mother, child, etc. and the only thing you can say is 'yes' or 'of course, as you wish' stuff, until she calms down (hormones in brain take about 20 minutes to dissipate) and becomes more 'rational' again. Then hopefully she will apologize if she was grumpy with you.
I know my own PTSD, although alot more mellow than it was a few years ago, can still be triggered in situations when other people have control or dictate my freedom of movement, whether that be someone blocking my parked or moving car, doctors in an ER not 'allowing' me to be released after an allergic reaction, or anything/anyone that can 'control' my well-being. She might also be sensitive to males that display bad tempers or yelling, be careful with that. In fact, with all the predators out there, most women are fairly nervous around men these days that cannot control themselves well.
Hope that helps. Hope it all works out for you.