How do you usually respond when she says something nasty?
Let yourself being guided by empathy. Real empathy for your BPDgf. When she says nasty things and/or is angry keep in mind that she is in a lot of pain. Pain that we cannot imagine. Read about which thoughts they have about themselves and the world. Especially when they're stressed or angry. Imagine being them. If you truly love her and keep those things in mind, you cannot have anything else than empathy and compassion for her.
Especially when she says nasty things. Don't take the words personally! As a matter of fact, try to not even hear the words. It's difficult, I know. Believe me, I know.
Her pain and thoughts are unbearable and all she does is shouting at you in order to ease her own pain. It's a cry for help, really.
And at those moments we need to shine. We need to listen. And investigate. Trying to figure out what she's struggling with. What she really feels and says. It has more often than not nothing to do with the words she says.
The other day my BPDso was shouting at me. Occusing me of things. Don't read that lightly, it was honestly very nasty stuff. Harmful, aimed at my personality, at me.
But it was all irrelevant. I knew by then that she was stressed about other upcoming events. So the first thing I said was something along the lines of, "I can imagine you are stressed right now. I am also stressed about the upcoming days. Is that right?"
I didn't say it so "text book" like that but the gist of it was the same.
I hope this helps a bit. It's very difficult to execute. But
it works. Responding like that flips a switch in them. My BPD calms down immediately when I respond like this. Our task is to be strong, calm and gentle. Especially when sh*t hits the fan.
That's when their strong significant other - us - is all they have.
When all things are in place, e.g. real love, and thus empathy, and knowledge about this horrible mental condition and the techniques and concepts that can be applied by us in order to deal with situations in the best possible way, and the urge to be there for our pwBPD, it will come naturally to respond calm. Because it's the person you love so deeply that's in pain. That's struggling.
Then all you can and want to do is be a lighthouse that can guide the ship that's sailing in the wild ocean without an emotional captain towards calmer waters. But you cannot take the steering wheel. She has to sail. But that light on shore is so important for them. It's all they have. If you forget to turn on your light, all they have is darkness.
Shine. You're the best lighthouse there is.