Originally Posted by youretooloud:
Talk to dad. Tell him Mom wants her off the list (with good reason) and ask him to find another backup for now, because you don't want to be caught in the middle, or be stuck with kids all night because of this.
He should understand why mom feels like this, and if he doesn't understand, he's a douchebag. (beyond the obvious)
This.
Don't even leave it an option. Let them both know because you are aware of the ensuing drama and don't want it to affect the child. If they do or don't want the other person in their lives that's their business to sort out outside of your care, but it's too much of a mess to be fighting over on your time or property. Let dad he needs to find someone else.