I'm terrible at ending a discussion without her blaming me for not caring
You can end the discussion by walking away from it if you must. There is no way to perfectly validate or use and tools to make the pwBPD never react badly, and never blame you for their mess up emotions.
All we can do is try to remove ourselves from the conversation, end the conversation, remember another task and leave, and find a way that works for you to refuse to engage. I try very hard to ahve a reason to leave the ouse for a few hours that does not look like I am having my own tantrum - I need to go to the store before they close. I need to go out back and mow. I need to fold my clothes. Whatever.
Since she is used to throwing you out, how would she react if you just leave? Just grab some items (or have a bag packed just in case, waiting for the next fight). And say, I am going to "leave and will come back when you have calmed down." Taking the power to kick you out away from her might shock her a bit. Go on phone silence for a while. It sounds like you try to talk to the end, and let her get all her digs in - that's not good for you. I know leaving is not always possible - I get stuck by my house shape and by the time of day and have to weather the storm, but if you can leave for a few hours, try it.
