I would not let her get away with the rumor mongering and the overall bad behavior. It's really not her family as much as it is yours and reven if you view it equally she has no right to bother and pester you as she does. I would say something to her to make her stop. You need to make a point. Because it's not right. She should not be so rude.

I implore you to make a point to her and anyone around you if you need to, to make her stop being so rude and negative. It's not good for anyone, your family and relatives as well.

What she is doing is not right.

Good luck.