Even if it does have anything to do with Borderline, that doesn't excuse her behavior. She was wrong.

That said - how many years ago was this? Holding a grudge does no good. Forgiveness does. Your hair can grow back, but do you always want to hold a bad feeling towards your cousin?

She screwed up. I won't say she didn't. And I don't know why, but the why does not matter. Let it go, and be at peace.