So: what next? After tossing it around, I think the main thing is that I should stand down a bit, and stop seeing certain interactions as power struggles. Or rather, stop treating them that way: I still think that part of what's going on is placing her in the role of provider and placing her children in the role of provided for; that is indeed a power dynamic, but it's up to me as to how I respond to that. She's older, she's set in her ways; if I can find positive ways to redirect her energy or attention, then great, but if not, I should think about what I want to get out of actively pushing back.
And yeah, I think her memory isn't what it once was. I'm not sure what to make of that, other than to be glad that I'm not seeing any signs of that with my dad. And to be prepared for it to get worse.
The bit about the different grandkids was odd, though. I'm hoping that it was a fluke.