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.
H 34 W 29 BD 3/12/18 Divorce Busted Spring 19
It is not things that bother us, but the stories we tell ourselves about things.