If I come across a "difficult" child, I try really hard to make friends with them by playing with them, showing an interest in them etc. I then find they are much more willing to do as I ask - just little requests like "can you help me put this away" or "let's not touch people with our shoes".

You could also do a more broad set of "behaviour guidelines" for the whole group to outline expectations etc. But this would still have to be done really carefully so it wasn't obviously all about this woman's children.

Someone also could quiety ask her what she would like them to do if her kids are doing the wrong thing.

Good luck - really tricky situation. xo