Thing is, bertrand, you're so very sure tabby was unreasonable. I thought so too tbh. But then her late post puts things in a different context. I still think that it's nice for family to see the kids on a birthday, though sometimes it just doesn't work out. But tabby's later post puts a different perspect it. Expecting to be visited all the time but it never being reciprocal when there are no fitness issues is a different story.
But I don't think it's ok to fall for some sort of game playing, which if you actually read the OP's posts, is what's going on. She's made it perfectly clear there was another family party that her MIL didnt want to attend, and that she can come -another- day, she's even said when and invited her for tea. SHe's also been clear that MIL will take over most of the day and mean all other plans have to be suspended.
This thread is astonishingly full of people cherrypicking, reading badly and refusing to accept anything other than their own projection. Maybe a few who genuinely think it's ok for an awkward woman to get her own way, no matter how much it means putting other
OP, I do hope your MIL gets to see your son near his birthday and that you can find a way to co-exist with her that is reasonable. I do think that the PPs who suggested actually being very direct are right "saturday morning doesnt work for us, please come sunday afternoon for tea, or we can come to you". Over politeness actually does no one any favours, not your MIL and not you.