There is the possibility here that the grandmother was given cold showers herself as a child and was using as a threat the worst thing that happened to her, but somehow it just doesn't sound like that to me.
How did the little girl react when given the threat? It's too premeditated for me, I too can understand ( but not condone)someone "reacting" but as has been said planning to cold shower a child is unacceptable to me. Exactly what is it going to teach the child other than the supposedly loving caring parent is bigger and stronger and can do whatever they want and make the child as uncomfortable as they want and no-one will stop them.
This scenario makes me concerned on several counts and yes there is a degree of speculation from all of us because we don't any of us really know the whole situation, Anna doesn't either.
A relative of mine has adopted children, she receives lots of help, but then she's the type to ask...
I wonder what the childs real mother would think of this situation, probably thinking she did the best for her child by having her adopted?
I think the teacher needs to be told what occured after she left. I freely admit I know very little if nothing about the french school system, but surely the teacher should be able to get some assistance for this child and her family? Even a referral if this child does have behavioural problems. It does sound like the family needs help.
Either way no matter what, what happened was not ok, personally I would have to speak to someone or my concience would kill me, as a last resort I would end up befriending the grandmother and trying to help her myself.
Sorry i'm rambling, shouldn't be on here i'm tired.