You have a right to your feelings and to protect yourself. It doesn't matter what your mother thinks because she isn't living your life. If you need to cut off contact with your father for awhile you have the right to do that and it's OK to establish boundaries with your mother too. My mother was physically abusive to me growing up and my father was emotionally abusive, I've had to cut off contact with both of them for periods of time in the past and I've had to put boundaries into place to protect myself. Right now I don't answer the phone if my mother calls me, I wait until I am in a good state of mind and mentally prepared and then I call her back. With my dad I see him when I feel OK with seeing him. It's hard because society and even your parents will try to guilt you into thinking you HAVE to do this, or that to be a good daughter or a decent person or that you owe THEM something. It's BS and don't buy into it. You owe it to YOURSELF to feel safe and no one has the right to hurt you.

If you aren't in therapy now I strongly encourage you to seek it out when you feel ready. It helped me soooo much with the flashbacks and nightmares. I found hypnotherapy particularly helpful but I don't know if that is the case for other PTSD cases. I am now back in therapy for the second time for cognitive behavioral this time to help with all of my other issues and I wish I'd done it sooner. There is help, you can get better and you don't have to live the way you are for the rest of your life, there are lots of tools to manage it out there.