Ugh, I've been killing myself for about an hour looking for this on google (which is bad, because I'm good at looking through google and finding what I want)

I thought maybe if I mention it on the blog it would spark someone's memory and they'd tell me what they know, so here goes the description:

I'm trying to find a book I read years and years ago, of which I don't remember the title or the author. The basic premise was there was a Noah-esque flood, and the family in charge of collecting the animals accidently screws up and leaves the unicorns behind, and that is why there are no unicorns today, they didn't survive the flood. Specific details: I think it was a young adult novel. The protagonist is this young woman who was (I think) riding on a bus or train or something, and she sees someone with a hamster or gerbil or mouse and the woman (I think) with the hamster had actually bought it in order to feed it to her cat. The protagonist thinks this is mean, and ends up buying the hamster off of the mean woman at twice the cost. Then, when the prot. gets off the bus, for some reason she's in the middle of a gang or something, and they step on the hamster. At one point she meets this nice stranger guy, and goes to his house, and (I think) starts falling in love with him. Anyhow, his family is in charge of the whole two of each thing. The unicorns they have are a couple who just had a baby unicorn. They couldn't catch the baby, so they just have the parents. The mom unicorn is so distraught that one night the prot slips out and lets her free to look for the baby. Soon the male unicorn starts dieng because it misses the female one so much. Then they let him out to look for her. They end up finding the dieng unicorns in a convienience store or something, and the flood starts, and i think the prot and the guy she likes are stuck there, or get out of there in the nick of time after the flood or something. Anyway, it's driving me nuts that I can't re-find the book.