Hello, Brianlost! Welcome!

I'm so sorry you're having to deal with this and, unfortunately, it's not unfamiliar to me or (I'm sure) to many other members here. My husband (undiagnosed) gets very angry at people and can hold grudges for years over the tiniest, perceived slight. I swear he also keeps a mental tally of any mistake I make and brings them all out when he's dysregulating.
Could you share a specific example or two of an incident? That may help us get a better idea of what's happening and what tools might be helpful.
One phrase you used jumped out at me: "even if she has been shown that she is in the wrong." People with BPD generally don't respond well to being "proven wrong." For them, facts=feelings. If they feel something, it must be true. My husband will twist facts every which way so they'll fit what he
feels must be true. Calling them on this rarely helps and, in my case, tends to just make him more defensive and upset. Validating feelings without validating the invalid is a very tricky skill (one I still struggle with) that can be very useful.
It's bewildering and frustrating for a rational person to deal with, I know. I'm frequently baffled. But by starting to learn how the BPD mind works, a lot becomes more clear.