I actually found something that seems to work.
I thought that when my GF has the emotional baggage of a toddler, I might break the issues I have with her behavior down to what a toddler might understand.
So I told her that every time she was insulting me, accusing me or whatever, it feels as if she hit me on the hand with a hammer. I said that I could try to absorb the blows (dealing with her), pull my hand away (leaving her) but that the best thing would be, that she would stop hammering.
She than said that I did the same to her. And I anticipated this. So I told her: 'If you hit me on the hand with a hammer, I will indeed push you away because you are hurting me, and that is also wrong, but if you would stop hammering, I would not need to push you away.'
The day after she even used my metaphor to put a hold on her behavior that was spiraling down again. she said: 'O, I think I'm picking up the hammer again.' At first I thought she was being sarcastic, but she actually turned her behavior around.
Not saying its waterproof, and it will work for everyone, but at the moment (3 days later which is a long time without any arguments) it still stands.
