Thank you ALL for your replies. I so sorry to hear that tou have been through the same kind of crap!
Ive woken this morning to feeling guilty! Why on earth i have no idea. I was reading your replis and thinking 'have i been too harsh? She is actually very kind' and my husband says he struggles to tell her where to go because he says she loves her GC so much that she is coming from a good place, albeit in the wrong way.
But then i thought, no, i am always upset, DH and i never quarrel except about her. To be honest we have a fantastic relationship and he is a very good man, but last few months as MIL behaviour has got worse he gets so defensive that it hurts me so much. I know he loves me so it really upsets me that he doesnt addressherbebaviour with her.
I thougbt back to other incidences - like she found a packet of smokes. She knows i only smoke when my friend from Abu Dhabi comes to stay, and she said 'well i will blame you when my GC start smoking' as if i would light up in their little faces. I am outside when they are in bed!
Ive not learnt that one of her other DILs cant stand her and the other one thinks she is 'obnoxious' so it isnt just me which is a relief because i was beginning to feel targetted.
I think her rude ess towards my mother was the straw that broke the camels back. My mum is fab - she is so kind and fun with the children that is why they prefer her. After posting my text last night i text my MIL in my temper to say that Mum had told me that mt son had upset her and that she had thrown her arms up in a huff outside the school and stormed off because he didnt want to leave my mum and that she didnt even aay goodbye and her response this morning was 'i was very hurt by his reaction' and a smiley face emoji? No apologies, just that she was hurt and had somewhere else to be.
She has told me that my son's spirited behaviour (which i love by the way - and he ia reidiculously loving and caring btw) is because i keep calling him 'my baby' and that he is choosing to act like a child 'because mum speaks to him as if he is a baby' for gods sake he is 3.
She has become so bitter and he face contorts because she is so angry all the time or judging someone.
But maybe all of this is not my feelings towards her, maybe its because i am so upset DH wont stand up for me. Would you expect tour husband to tell her where to go
These are just small examples! I cam bring so many other things to mind (she gave us 1.5k towards a 10k landscaping job and when he didnt turn up to finish the job my MIL said she was going to tell him because she had contributed to the cost and so she had every right...) The school dont have her number, she went there of her own volition and the headteacher thought i shouldve knows about it. She has now gor the hump with the school as she didnt feel she was listened to and they didnt give her a thank you note when she donated supplies to them. She is fuming most of all that they dis not return the bag that held the supploes back to her 
Thank you all for giving me advice - means such a lot today when im feeling so upset