I had/have a MIL like this too. The most upsetting thing was when I was still in hospital post CS and she TOLD me that my SIL was coming to see the baby at home the following weekend, it was the way she said it and the look she gave me like I had no say in the matter. I agree with a previous poster who said that feeling out of control does lead to PND and this certainly made me feel like that. I still feel upset about it to this day. There are many other things too but I agree you need to nip it in the bud, I did it by being unavailable for a long time and then letting DP bring the children round to hers. As mentioned by somebody else this saved my mental health too. Wishing you luck.