Thanks to everyone who wrote in to let us know Yale has been limping. We will eventually respond to you all personally, but it may take a little time.
We checked her out ourselves, and we're convinced nothing is broken; she probably just twisted it a bit when she was climbing and playing.
We're going to take a watch-and-wait approach for the moment. There's really not much a vet can do in this situation anyhow. But if she doesn't seem better in short order, we'll take her in regardless.
EDIT: It's Monday night, and Yale is still limpy. If she doesn't seem better in the morning, we will take her in to a vet.
Here's a quick photo to pay the cat tax: