OK it is late in the afternoon now and I am still in pyjamas, I need to go and buy some food!
Thank you for your replies, I posted here because from what I know, in the UK there's a more "normal" relationship between women and their MILs so I was hoping for some back up and many many thanks to the posters who gave me that and understand my position. Actually the YANBU % is quite high so I feel positive.
I don't think we always need to smile sweetly and accept being disrespected which is often how it feels with MIL. I admit I did lose it and maybe it should have been a little more diplomatic, but also it doesn't do any harm for her to realise that I won't accept "digs" any more. Why should I? I love my DP, I'm glad he is a good son who cares for his mother well, as he does for me. I'm glad she has a good relationship with him too, for her sake. It's fine if he sees her every day, yes maybe a bit annoying in some way, but I accept this is his choice.
So with that in mind, why give me those digs? Why when you have everything you need, try and then also have a little slap at me? Why not be happy you have a "DIL" who is usually quite chilled out with all this, when he is getting up at 8am on Sunday to go and do her garden, when he is driving her to a hospital appointment, when he is always doing X Y and Z. Just be happy I don't make a big deal out of this?
With the lunch comment, when I said "he can organise it himself", she could have put her hand on mine and said "I know. Maybe it's silly, but in some way it makes me happy". Then my heart would have melted for her. But no. Instead she chooses to make it a power situation and this is the root of the problem.
I don't believe it's my role to take disrespect from my MIL just because she is his mother. It doesn't make me a bad person. I'm not horrible or nasty. But I should be shown some respect because just as she is his mother, I'm the woman he has chosen for himself. We both deserve equal respect from each other.
I think I will tell DP all of this calmly and I think I would also like to calmly if possible confront her and say all of this to her directly. I will keep you informed if there is any interesting news 😅