I managed to get an appointment for early afternoon, which is a relief. The vet poked and prodded her, weighed her (15 grams), accidentally let her fly away (most of my birds manage to do that!), plucked a few feathers off from around her vent area (ouch!), and presribed an antibiotic. With such a small bird it's hard to tell anything for sure, since you can't draw blood for tests, but her vent was clearly messy, so there's something going on. Hopefully those magical antibiotics will take care of what's ailing her.

I just know she's looking forward to getting smeared with pink stuff every day.