Update:

Pepper (my 10 y/o female) has been at the animal hospital since Thursday. She developed a very bad skin breakout that the vet currently thinks may be a severe staph/bacterial skin infection covering her entire body.

She seemed to be doing OK at first, but this has rapidly progressed over the past week as she did not respond to the milder antibiotics she was initially taking. When I got to visit her today, she could not even stand up. They are running all kinds of tests, but so far the only results they've gotten are telling them she has a severe infection, with the skin being the only obvious source (not kidney, etc. - all those tests are basically negative.)