Take pics of the damage and send her the bill plus a list of the missing items. She would not be welcomed into my house unless she is monitored to watch the kids and asked to leave if she did not do it.
I had a church friend who came over a few times as I held a meeting there. I told her she HAD to disipline as I could not be liable if they got hurt.
The meeting was difficult as it was interupted many times. she had problems controlling them. Suggest to your son to have the tv Nanny come over to teach her how to parent. Where was he?