I drove rhekarid over here to pet her today. She was happy about having company, but not quite fully awake - she played a bit, but not with a full level of energy. She was never really fully active at any point today, and she hasn't been eating very much today either. I gave her some canned kitten food, and she extremely eagerly gobbled up about a third of the can right away, but then she stopped, and she never ate anything more than that the whole day long. Even when I wave the canned kitten food right under her nose now, she won't take a single bite.
Based on this chart of symptoms of the most common "cat flu" viruses, I'm just about positive she has the feline rhinotracheitis virus (a.k.a. feline herpes-1 virus). Which means she's likely to be sick for about a month, or possibly longer because she's a kitten.
I don't think she's in any particular danger of death so far (I've had several sickly kittens who died before, when I was a kid, and Stardust does not seem that sick), but if I can't get her to eat more tomorrow, she's probably going to need to go back to the vet. Not that the vet can do much for her, really; he was just going to give her antibiotics, and they aren't going to help a whole lot if a virus is the main thing that's making her sick. But if she doesn't eat anything, at least he can feed her intravenously.