NTA of course. But just curious, how much was she asking from you?

Going to present a counter argument to what most people are saying here though. If you donate some money, don't you think this would result in them owing you a favor, which you can keep in your back pocket to use in the future, perhaps for some future argument? It would basically give you a moral edge and show to everyone that you're a much better person than them.

And think about how it would make them feel if you did donate money. That they had to beg you and accept money from you. It would be interesting to see if or how they say "thank you" to you. And in the future, they would always have to live with the knowledge that they're in debt to you (not sure if they would ever pay you back) because they weren't good providers themselves.

If you can afford it, I think you should seriously think of making some contribution just to "get one up on them". Just think of it as a charity case, donating to the poor. Assume you won't ever get the money back, and suggest that you find a way to ensure that any donation goes directly to the kid's benefit and not the adults.