ESH except the child. Yes, I know she is turning 18, but still a child.

You should have stayed out of the situation. Yes, she was in your driveway, but this had zero to do with you. It was between your husband and his ex wife. You want to rant about her after she’s gone? Rant away, but never get involved in the moment.

My husband had a terrible ex wife. She was a constant source of drama, but I never rose to the bait. I’d fume inside while my husband dealt with her. He also never involved himself in issues between myself and my ex husband.

It sucks, but by stepping in, you have caused an issue with your step daughter. While I don’t blame you for wanting to cancel the party, it’s not a good look. She did nothing wrong here and she is the one being punished.