I've namechanged for this as it's probably fairly outing.
Just to clarify I love my MIL. We have an incredibly close relationship and we get on great. That being said she DOES do/say things that grate on me occasionally but I guess everyone does. However,
In order to not drip feed, back when my DS was born in September we were both very poorly after labor. He had a bad infection (they think meningitis) so was on IV antibiotics for week and had to have a couple of lumbar punctures. I also had a bad infection and lost a LOT of blood and needed 2 blood transfusions. The week post birth was a bit of a blur! Baby was born on the Friday. MIL met DS as soon as visitor times were allowed on Saturday. She was due to come again on Sunday afternoon but due to me being poorly and PND (they had yet realised how poorly I was) I had a slight breakdown on DH and DM about being stuck in hospital, wanting to go home, the stress of DS being poorly etc etc. DM rang MIL and said to not come to visit and I was unwell and not fit for visitors. MIL told my mum I needed to 'get a grip' as being a Mum meant no time out.
Let it slide. I was upset DH never defended me against MIL but whatever. That week DH had to say with me in private room as I was struggling and DS needed taking for regular antibiotics. I never once was told I was doing a good job. Never once asked how I was. Instead was shoved down my throat about 'DH is so Lovely staying with you. I bet he's so tired. He's amazing' etc etc. I was too poorly to notice it at the time (and use to it 🙄)
Now whenever any of us is poorly (as small as a cold) it's 'suck it up fullofhormones, no rest when you're a Mum'. If DH gets it, it's 'oh poor DH. Having to go to work. And then come back to baby. Do you need this? I got you some tablets' etc etc. You see where I'm going. I get he is her son so she is bound to care more but sometimes I'm a bit  because more than likely I gave him the cold he's now suffering so much with.
Small things, like DS needing gaviscon upping for his reflux. She told me he didn't. Rang the drs (she works closely with them and if she rings we get it quicker) to order new script and didn't order higher dose even though I asked her too. I asked her why and she said he 'doesn't need it'
He needed his formula changing. I told her and she said 'no he doesnt'. Told her I was going to change it and she brought me 2 tubs of the normal stuff because 'he doesn't need it changing'.
These are just examples, I'll stop now as this post is already massive. However we recently had to move back in with PILs to save for a deposit, which I am soooo grateful for. They've helped us out no end. However I knew this would be hard but otherwise we would have been stuck renting. DS was in a right tizz last night after having vaccinations and he was crying a lot. We have our own lounge so we get our own space but she barged in asking what was wrong with him. I just said over DS screaming in my arms whilst swaying him round the room he was unwell. She then stood there at the door watching me trying to ask questions. FIL then appeared and they both just stood watching me trying to soothe distressed son. It really stressed me out.
I can't explain it. Writing it out now seems really silly. I know they were worried about their grandson as he normally is so quiet but something about them both staring at me trying to soothe DS really bothered me. Myself and DH eventually got him bathed and into bed but it upset me so much I cried when I got into bed 
AIBU and it's still my hormones that haven't settled or would that have annoyed anyone else? I can't understand why she's said and done a lot worse and I've let it slide because I do care a lot for her but something this small tipped me over the edge! Thanks for reading if you got this far. Sorry it's massive