I normally don't post things like this here, but since I posted about the cat yesterday and alot of people read that (and emailed), I thought that I should tell what happened.
We took her in to the veterinarian today. After checking her out thoroughly, the vet stated that everything that she saw was consistent with advanced cancer, and that there wasn't much that could be done. After talking with the veterinarian for a while, we decided that the best thing to do for Missy May was to euthanize her - she was cearly weak but not yet in much pain, very old, and her odds of improvement were pretty much nonexistent.
Both Kaylia and I are pretty upset. Still, we made the best choice we could with the information that we had on hand. And, in the end, Kaylia wanted to take Missy-May in so that in her final months the already elderly cat would be happy and comfortable. Kaylia succeeded far better than she could have expected.