Problem: 29 year old nurse presented to the PMHNP for evaluation after a traumatic event. Two weeks ago, she was attacked by a patient on a behavioral unit where she works. She says she is having flashbacks about the event and keeps wondering "what could I have done to prevent this? " She has had several panic attack since the incident and she is to the point now where she is considering quitting nursing. She said, "I guess I am too weak to be a nurse if I can't handle one attack. "What is her most likely diagnosis?