If that means that the daughters can't play together then it is what it is. That lady is being real fucked-up, and she doesn't deserve for y'all to even engage her. She'll probably just lie, go passive-aggressive and play the victim anyway.

I've had other parents run and scoop up their kids and get ghost as soon as my son and I show up at the playground, and while it stings, fuck those folks. THEY are the ones acting like assholes.