She won't go to a therapist for now, but you could. You are in a stressful situation. Also a therapist can give you ideas on what to do when your loved one is not stable.

A therapist can help air out your concerns, keep you on a healthy track, and make sure that you aren't getting too swamped and enmeshed by the situation.

I think you might be taking on too much responsibility. You cannot, and should not be in the role of therapist/ sole caretaker. When she pushes you away, you may need to respect that boundary setting, even if you don't think it is good for her ultimately.

If she trashes the apartment, she may need to then deal with the consequences of that.

A good PTSD book will have ideas for her on how to ride through triggers and flashbacks safely.