Don't scratch your head wondering if you've done anything. You haven't, you really haven't.
See, with this jealousy rooted behaviour, it can't be rationalised - because it isn't rational !
Boundaries are very important (they'll be individual to you ) have a think what yours are , then stick to them.
Keep being you and going about your life as you wish. Don't jump through hoops modifying your behaviour to please her. You won't do it. She'll move onto her next petty annoyance.
Trust me, this is jealousy. Does she only have sons/grandsons by any chance? I often find, for some reason, mothers with only sons tend to be the worst culprit for this type of behaviour. They seem to see a DIL coming along as a threat to their position in their son's importance list. And I suppose, in effect, it does alter. But it doesn't mean the son no longer loves his mum. A wise woman knows this. An emotional immature/,jealous one won't accept it and will instead lock horns to retain "top dog ".
It's very confusing and frustrating got a DIL like yourself who's not looking for a tug of war !
I have my fingers crossed that your MIL mellows. There is hope : mine really did. And truthfully, if she died, I'd miss her in our lives. Once upon a time , I was wishing some awful things on her. Babies do bring out the worst in a jealous matriach (further competition) and good source of wind up to play games with DIL.
Keep being nice. Don't react to any bait (it's hard, but it pays off) all games need 2+players. Don't be the second player. It'll get boring for her. Act naive and oblivious to any passive aggressive provocations.
Do some googling on ways to handle her. I strongly recommend killing with kindness and your own version of ',grey rock ' for the interim