I don't want to keep you all on the edge of your seats, so here's the news: Domino has a hyperactive thyroid. This is what's causing her lack of appetite and weight loss. We're going to put her on a low-iodine diet and hopefully this will clear everything up. She also got a flea bath today, and tomorrow I'll de-flea the house. That should take care of her flea-related itchiness.
With any luck, this will fix all our problems. All our cat problems, anyway.