Hi dan -
Your fiancee is lucky to have an understanding and supportive ally.
My advise is to reassure her that the trauma she is experiencing is not her fault, if she needs such reassurance; to help her avoid triggers as she identifies them; to let her know that you may not understand what she is feeling, but that you believe every word she says about what is going on in her mind and in her body; to encourage her to let you know what she needs from you, and to give it to her if you can, or explain kindly if you can't; to urge her to continue therapy and to try medication if her therapist and doctor think it would help; and to be a buffer between her and family friends who may expect her to "snap out of it" or "stop feeling sorry for herself", to name two of the unwittingly cruel things that people may say.
You have posted two identical posts. We ask that people not do this, so I am going to remove the one from the introduce yourself forum, and leave this one where it belongs, in the PTSD section.