PrammyMammy - I know how it is to have a difficult, manipulative MIL. Sometimes it is very hard to say things to her. (Although thank goodness mine never offered to suckle my children!)
My MIL thinks I am a dreadful DIL whatever I do, and believe me, I used to try really hard. It sounds to me like yours will be the same. I just gave up trying hard and pandering to her.
Things came to a head one day, not too long ago, when I had had enough of her constant criticisms and insinuations about my lack of parenting skills (and she could be very subtle, so if I said anything it made it look like I was the one with the problem). She had just told me to smack my son (then 20 months) for biting. I refused and told her I had a different way to deal with it. She started muttering about foreign people being rude and uncouth and how families were much closer in her culture. This is very relevant, as I am British and she is Greek. She had made racist comments before, but I had brushed them off and tried to be tolerant.
This time, however, I just lost it and shouted at her in her own house. I really put her in her place, and then I took my children and left. DH came storming in a few hours later, having heard her side of the story. I told him that if he wasn't prepared to support me then he could ring his mum and thank her for having caused his divorce. I don't know why, but we both burst out laughing, and he phoned his mum there and then and told her not to come round until she had apologised to me.
However, what I would say to you is don't let it get to that stage. I had put up and put up, and eventually things blew up over what should have been a trivial incident. You don't want to be in the same situation. I don't want to cause problems between my dh and his mother, and I'm sure you don't either. Best to nip it all in the bud now. Talk to her calmly and firmly over a cup of tea, try to find a middle ground before it escalates.