She's been having trouble walking for a couple years, and her hind legs have obviously been giving her more and more trouble over the last several months, but now they seem to have reached some kind of literal tipping point. She keeps lying around with her hind legs at angles that don't look natural or comfortable, as if they aren't even part of her body. She's completely limp much of the time. She peed all over the Cat Bathroom floor last night, right between two litter boxes, and I have to guess this was not her usual "peeing in odd places" behavior, but rather that she can't climb into a litter box anymore. (She likes to lie in boxes, and I've noticed just in the last week or so that she was having more and more trouble stepping her hind legs high enough to get into them, and would often stumble awkwardly and then give up.)
Last night, while we were asleep, despite peeing between the litter boxes, Cobweb somehow managed to jump up onto the love seat in the next room, where I found her this morning. So her hind legs must still have some life in them if they can propel her onto furniture.
But Shannon and I agree that it is probably time to take her to the vet for the last time. We're going to watch her today, give her a chance to bounce back if that's possible, but we aren't very optimistic.
Instead of going to Lisa's house today, I've invited her to come over here, if she doesn't mind hanging out under a shadow with a friend who is preoccupied with a nearby stripey cat. She apparently doesn't mind, so I can keep an eye on my baby much of the day. And spend some time with her, when time is running short.