yellowxo this situation could destroy your relationship. So what to do?
Firstly, something about your MILs behaviour. If your MIL hasn't had a GC before and this is her first she will be totally smitten by your child and may not realise clearly how her behaviour is impacting on you. So I am afraid that you need to tell her.
When I had my first GC I was madly in love and had to be very careful as I thought I knew better how she should be treated. I was after all a very experienced Mother. To stand back and let my inexperienced DIL make mistakes was very hard. I hated to see my GD punished and still do.
Unless your MIL is deliberately setting out to undermine you ( and is thoroughly evil) and wants to hurt you, then you have no choice but to tell her how you feel. My DIL is very capable of telling me and I respect her rights. I would rather be told than get the cold shoulder or worse break up my sons marriage.
Most people ( I was) are inhibited by their MIL and can't relax and behave normally around them ? But what is the alternative to telling her ?
You can work hard on going non-contact. This will make your DP unhappy, it will also deprive your children of someone who will love your children.
Ideally it should be your DP who should be telling her, but as you say he won't , so then it is up to you.
Prepare a script. Stick to the 'i' word, rather than you , as in, you are an interfering old bag and I hate you etc. speak in sorrow rather than in revenge or anger. Think about your aims in doing this. It is to stop her doing what she is doing, not to make her scream and shout and storm off.
If she has any sense, then she will listen. She is in danger of losing your much loved child, because if your relationship with her son breaks up you could leave and go and live as far away from her as possible. If you don't give her the chance to change then she will never know. Your relationship will break up because of her, but she still won't know about her contribution because no one said anything.
I think you have to give her a chance to change.
If you don't stand up for your self and say your piece, your anger and frustration are going to increase. You will then explode and say things in the heat of the moment that you can't take back, and then there will be no going back.
You need to make a list and sit down with your partner and calmly and quietly tell him how you feel and why you feel like you do. Explain to him the danger your relationship is in. If he starts arguing just carry on and keep to your script and then move on to her. Unless her agrees to do it at this point.
You could also do with some counselling so that you have more self esteem, so that you are able to set boundaries and insist on being respected.
If your MIl realises that if she doesn't change her behaviour then she may lose seeing her GC, that may be a wake up call for her.
Good luck, because the MIL, DIL relationship is not easy. Xx