Oh ransom, you are in a difficult situation.
What you describe in your posts is someone who right now doesn't know how to be in a healthy relationship. She currently does not have the 'tools' to be a healthy partner, like communication skills, self-reflection, taking ownership of her own feelings and thoughts. Those are necessary for any relationship - poly relationships just take more of all of the above.
And maybe, you don't either. At least to be in a healthy relationship with her right now.
You do realize that just about anything you say or do may trigger her? I'm sure you don't poke at her hurt places on purpose but that is one of the vicious things about abuse. It fractures people in ways they don't always fully realize - until someone, usually innocently, blunders into that fractured, hurt place.
That is an awful, awful thing that he used psychology and therapy lingo to control and convince her she is fucked up. It is not right, it is not fair, and she did not deserve that.
But a real, ethical therapist will do nothing of the sort. A good therapist will listen to her, provide some perspective, and support her in healing. It might take a while to find a compatible therapist - that's common. But she needs someone who is not a friend, a lover, a family member, to listen and hear her. There are also support groups of surivivors that could prove useful to her.
And bluntly, she is fucked up. That is what abuse does. It destroys, rends, tears at a person's soul. It makes black white and vice versa. It pulls apart a person's ability to tell reality from lies. It erodes sense of self and destroys confidence. She did not deserve this, it was not right, it is not fair.
She needs to heal, to find out who she is again, to understand her triggers, and learn how to manage emotions. We all need to do this in life but it is especially critical for abuse survivors. To heal and truly move on, survivors need to face and understand the abuse. (And by understand I do not mean forgive their abuser but rather understand the patterns in their life, their behavior, their abuser's bahavior that contributed to the abuse. Seeing the patterns in one's life that make one vulnerable to an abuser does not mean that abuse is ever their fault.) That requires a lot of work, pain and time.
There is also the risk that she will be abusive. I am not saying that she is currently abusive or abusive to you. But I do see a pattern of emotional inconsistency that could turn into full blown emotional manipulation. Your fear of triggering her, while understandable, is worrying.
Finally, and this may be hardest of all for you, YOU CANNOT FIX HER. You can't. You can love her and support her and encourage her. You can model good healthy behavior for her; you can be honest and loving and geniune. All good things. But if she is unwilling or currently unable to do the work necessary to learn the tools she needs to be a healthy partner, a healthy person, she will be unable to be the partner you deserve. And you do deserve a healthy partner. She did not deserve the abuse she suffered nor the damage that it caused. But you deserve a partner who is capable of being in a healthy relationship with you. The poly/mono stuff is really secondary at this point. Is she able to be a healthy partner for you? Can you do the same for her?
If the answer is no to either, then it is time to end the romantic relationship. Give her and you time to heal. Be friends to each other (while realizing this may be hard). Once she, and maybe you, are in proper working order, perhaps there is a chance of being in a healthy, loving romantic relationship. I hope so.
I know you love her. That is very clear. But love is not enough by itself to make a relationship healthy. I wish you and she the best.