Okay, so after nearly two days with me (well, two days and one night), the little gray cat still hadn't eaten anything, or drunk anything, or used the litterbox (or the floor, although I'm not so sure about that part). She spent the entire day while I was at work hiding under my bed, as far as I can tell, and I spent the entire day worrying about her.
So when I got home and realized she was making herself sick rather than deal with the move to a new home, I called her former owner and asked if she could take her back. And thank heavens, she did. I feel guilty about this, but on the other hand the woman has another cat (actually, she has ten) that is more outgoing and needs a good home. So she took the little gray cat back tonight--and the cat is thrilled to get back to her person--and Wednesday night she's bringing the other cat over.
It's a cat swap. Like a cookie swap, but with more claws.
So now I feel guilty and sad, because she was a sweet little cat. But I am not really emotionally prepared to deal with a neurotic animal right now. We'll see how the other cat does. Probably a good thing I didn't get a dog, huh?