That is an interesting thread you linked to. This one might be helpful too in helping to understand why anger is common. It is a defensive response, along with flight, freeze (dissociation), and fawn (co- dependency).
https://www.myptsd.com/threads/figh...tions-to-trauma-inflicted-in-childhood.10484/
Your friend is using these defenses... And is abusing you and ignoring the real issues. It is sometimes true that hurt people hurt people...
PTSD and anger are linked. It does not make it ok. Depression and suicide are linked. Depression doesn't make suicide ok... It is helps explain the behavior, and it helps explain why boundaries against abuse and suicide are all the more important for recovery and for survival of a relationship while someone battles PTSD and/or depression. (The depression thing just being an example)
I want to tell you about one of the most healing and best things anyone has said to me was, "I want to talk to you, but you can not scream at me. I'm not going to talk to you until you are calmer and can tell me what is making you mad in a calm manner."
My friend wanted to hear me and also cared enough to not let me be an abusive jerk to her.
My anger comes from trauma and my friend did something that triggered PTSD related anger... but it was not going to help me heal from the trauma to let herself be victimized by me by stating in communication with me while I was still actively being abusive to her.
I am still friends with her and I am so thankful for what she did. It helped me have hope. She thought I could calm down and talk it through when all I saw and felt was rage. She did not outright challenge what I was angry about in the moment, and she was smart not too! Just like you. I was trying to push her away in a terrible way, but she didn't abandon me, just like you with your friend.
That kind of anger isn't of a logical rational place where I'm using all of my executive functioning. She also didn't abandon me. But in the moment she held a clear and bright boundary. She told me she would talk to me later when I was calmer. She hung up. I was furious when she did... and mostly scared. I immediately emailed her and said we would not be friends... really I was thinking I had really screwed up this time and she was going to reject me. She emailed back asking me to think through my decision and if that's what I wanted, she would respect it. She knew I had PTSD and knew my anger was related to it. She wouldn't let me scream at her but she wanted to be friends and work through what she had done. She was humble too. She wrote that she probably did make a mistake and wanted me to tell her what I had done to make me want to push her away.
I did eventually calm down and apologized and took responsibility... She forgave me and we worked through what made me angry to begin with. We became even better and closer friends.
Few people have the capacity to do what my friend did for me... but I tell you this to try to show you, someone having PTSD is cause to have even more clear boundaries, not to allow them to be jerks because anger is linked to trauma.
I know you care about her... if you can risk telling her no, I won't let you be abusive because it does not serve you or me, you will be helping her! She may push you away more... But the most amazing friends are the kind who are willing to hold boundaries and not allow abusive behavior while not abandoning the person (if this is possible, and it's not alway possible or a good idea. Sometimes the abuse invades boundaries and that should mean an end to the relationship.)
I still struggle with anger but have made a lot of progress since then. I don't scream at or be a jerk to my friends anymore. Instead, I'm now sometimes screaming in my car alone, about the actual trauma and working through it, while building healthy relationships.