We think Agnes had a small stroke last Thursday, possible caused by a clot due to her compromised heart. She fell on some ice when walking on Wednesday night, but got up and seemed fine. Thursday morning we went for our walk and everything was normal. I got home at lunch time Thursday and she was stumbling, falling over, and her head is tilted. Of course, every vet was closed for the holiday and I was sick as can be myself, so I waited until Saturday morning to get her looked at. Honestly, it really wouldn't have mattered if she'd gone in Thursday because there would have been nothing any vet could do except tell me to keep an eye on her. She has some tissue loss on her skull, her eyes aren't steady (they are kind of googly now), and she suffered some nerve damage. Her hind legs are not as steady as they were and the bent over paw test showed more damage on her right side.
The good news is that the vet told me that dogs have more collateral blood vessels in their brains than humans and can re-route the blood, so she will make some semblance of recovery. And she has. She is not as steady on her feet, but not staggering or falling over like she was a few days ago. So here we are, taking it one day at a time. I was definitely reminded that, despite the improvements that we've made, she is still a frail little old lady.
ETA: vet thinks it was coincidental that she fell and then had the stroke, that the two weren't related.