Just point blank tell her you won't be her friend. It seems like she isn't understanding, or doesn't want to understand, you showing her that you won't be her friend. You're there for your kids who are your world. I'd even say that to let her know what's important to you and it's not her.
Don't let her talk to you like that either.
^^^THIS^^^ Tell her you don't mind her going to the kids' events at the same time as you, but that you're both there for the kids, not for each other.
