I would say, "Your father's parents, your other grandparents, want to meet you. What do you think about that?" If she is interested in meeting them, then say something like, "Well, I don't know if they are the best people in the whole wide world, they sometimes say mean things and are kind of weird, but maybe they will be nice and you will end up liking them. Let's give it a try. If you don't like them, you don't have to spend time with them."
At 9 years old you can be pretty straightforward about it, and if they turn out to be wackos, then she doesn't have to continue seeing them.
I don't see why it should harm her. She has enough people who love her, testing out her other grandparents shouldn't be too traumatic.
Stop stressing about it. You are putting your anger and disappointment on her. She will do perfectly fine in life with only one good set of grandparents. There are lots of well-adjusted people walking around with zero grandparents.