There is no doubt that the tragic end of her previous relationship could have caused ptsd and/or difficulties with intimacy. Still, I wonder about the exclusive focus on her and her problems in this post.

You noted that she became frustrated over your lack of availability and skeptical that it would improve. You acknowledge that you fell short as a boyfriend, for some months. Her vanishing therefore may not have been "out of the blue"; perhaps it was simply the culmination of her frustration.

I wonder therefore whether it might not be useful to take honest stock with her of where you have fallen short in the past, apologize to her, and promise to do better now--not next semester.