Update:
The vet's diagnosis was distemper. But apparently, vets in Mexico have begun treating distemper with antibiotics and short term azathioprine after a two-year study showed a pretty impressive cure rate - 90%.
http://www.campusveterinariosenweb.com/file.php/1/moddata/forum/14/40941/EFECTO_ANTIVIRICO_DE_LA_AZATIOPRINA_EN_CASOS_DE_MOQUILLO_CANINO.doc(in Spanish - I haven't found an English translation, and Google translate isn't great, but if you can read Spanish, it makes a good case)
Those are pretty damn good odds. Hyssy got her first dose on Monday, she'll go back for more today, Friday, and next Monday, and in the meantime I'm giving antbiotics and eye drops at home.
If you looked at her today, you'd never guess she's sick. She bounced right back to 100% yesterday! She has her energy back, and her eyes are much clearer! I can't believe how fast it's working!
Who studies drugs in the USA for veterinary uses? Is it the FDA, or something similar to approve stuff like this? Or is it less regulated with drugs for animals? Man, they need to get on it and start studying the use of azathioprine against distemper in the states. It's a miracle. I'm so happy my puppy feels better! <3