Just for background my DM and I have always had a rocky relationship. I moved out when I was 15 because we were constantly arguing. Relationship got back on track when I was about 21/22 and has improved ever since. I'm now 29.
She constantly runs me down. Upon reflection I think she's always done this, but I'm noticing it a lot more these days.
She always says it in a cheery way, so it doesn't immediately come across as bitchy or aggressive, but it constantly feels like I'm not good enough.
Some examples:
Over recent half term. DM walked into my house and wanted to know why DS1 was there and not over at a friend's house? Why had I not invited one of his friends over?
For DHs birthday he wanted to go out for a meal at a restaurant and take the kids swimming. This is what DH wanted, Just a nice chilled family day together. Mum wanted to know, why had I not sorted something better for him?
A few weeks ago I went shopping with Dsis and DM.
DM wants to give DS1 a mobile phone. I say no that's ok, (he is 9) we have agreed he will get a mobile before big school. DM and Dsis persist in trying to get me to take the phone. I say I will take it then but keep it for another 20 months until DS1 is starting big school. I say DS1 has enough screen time and it's a battle limiting his Xbox use (he gets an hour a day) Dsis and DM laugh and say that frankly that's more of an issue with my parenting.
DM asks when the tutor is coming out for DS1 I say tutor has seen his latest school report and feels he doesn't have to come out to assess DS1 until December. DM and DSis are appalled at this and want to know why I am not more on top of this? (Rang tutor later that night and he reassured me that it was all ok, I was in his book and there was no cause for concern.)
Once when DS2 was teething and dropping his midday nap at the same time we were having a really rough few days. I thought I'll go to DM's house for some support (mistake). When I was there DM and Dsis actually asked me why I wanted more children when I can't cope with the ones I have 
(tinkly laugh).
Today everyone in our house has a nasty chesty cough. DH and i have been up all night ourselves coughing, and with a very unsettled DS2 (aged 2) whose cough is worse. DM says she's going to call over at about lunch time. I am knackered and I'm pregnant, but I clean the house to give her nothing to complain about. She walks into the house, DS2 coughs and she says "shame! Your mum really should have lit the fire" (central heating is on and has been on all morning, it's not a cold house). I say nothing but walk around her to reach my cup of tea and cough as I pass her. "Oh boy laying it on thick!" She says. At this point I feel a bit like crying and just walk off and leave her with the kids and DH.
I know none of it is really nasty, and as i said it's always done in quite a laughy, jokey type of way. It's worse when DM and Dsis are together. I just find myself now really panicking when I know DM is coming over, frantically cleaning, trying to leave no room for negative comments. But she finds something. She always finds something I'm not doing well enough.
It's a complex relationship. She is very kind in lots of other ways, invites us round a lot, loves my kids etc. It just seems that she can't help herself when it comes to passing nasty remarks. Am I being overly sensitive?