Sometimes people do something called
transference <--- Wiki link. Transference is assigning a trait from someone in their past to a new person, regardless if it applies or not. I don't know your situation, but this may be something to think about.
Example 1: I have never hit my wife in anger or intentionally. My wife coming from an abusive past, sometimes freaks out if my hands get too close to her face, thinking I am about to strike her.
Example 2: My wife's father was, um, less than faithful to his wedding vows. My wife has severe trust issues if I am alone with another woman regardless of the setting or situation. I have never given her a reason not to trust me, but because of her past, she thinks ALL men cheat and have affairs.
Example 3: In arguments from long ago (she doesn't do this much anymore), I would realize after a while she was not arguing with me, what she was saying, and bringing into the argument was issues from past relationships. This was VERY difficult for me, for a long time. How could I win an argument that had roots with other people, and what THEY had done to her. Not me.
As I said in my previous post in this thread. I strongly suggest that you don't try to "fix" her. If your interested in keeping the relationship going, simply roll with the punches, and let her know your there for her. This takes the patience and humility of a saint. Encourage, but don't demand she seek professional help. Even couples counseling. This may take a while, a long while or never for some people. PTSD is a lifelong journey, are you willing to join her on this journey knowing it will be a lifelong task? It can be difficult or near impossible at times. The rewards, I can not describe with words because it is different for each person. Some people are cut out for it, others... not so much.