Originally Posted by cadysmom
To me the bottom line is if family actively HURTS my child, they aren't family. Just because DD's brain is getting slapped around instead of her physical body, I don't see the need to allow that.
I would say exactly the same in your place.

I'm sorry that your sister's negligence is creating this pain for your family. I think you're justified in withdrawing from the relationship until they make a sincere effort to correct your niece's behaviour.

What is to give light must endure burning.