Anonymous wrote:OP here. Thank you everyone for the input.
I think I just got totally blindsided with this because normally my MIL is very reasonable and hands-off (she makes zero comments about how we've chosen to raise our DD, our choice of house, jobs, family size. Even during Christmas visits, we are expected to be there for meals but other than that, we can spend as much or as little time with the family as we feel like). She is basically the opposite of pushy, normally. She even gets along well with my own mother.
So this basically came out of nowhere. I think it may be a factor of getting old - a lot of people, my parents included, seem to dig in their heels more as they get older.
OP - if this reaction is really totally out of the blue for MIL, please ask your DH to talk to his mom and try to figure out if something else is bothering her or if she's feeling okay. Weird personality swings (especially in older folks) can be a sign of something more.