It's coccidiosis!
Fecal float test confirmed. Had to drive 45 minutes away to the only feed store that had any Sulmet... but we got it.
Lillith had actually improved by the time we got back. Whether it was the mash we'd gotten down her earlier, or -as the vet said- she was just getting through the worst of it, I don't know. But I actually saw her eat on her own a minute ago.
Through the state vet, a fantastic poultry guy at the state university has been emailing us. He just called me and explained that even in a really clean brooder set-up, the parasite probably exists, and can go through several life cycles w/o causing any harm until just the right environmental conditions cause an explosion. What conditions? "Warm and damp" he said. Ohhhhhhh.... like last week when the chicks spilled their waterer and it was 80 degrees on the porch and I didn't notice for 5 hours how wet the bedding was? Exactly.
So much for 100% organic! We're putting the 4 chicks on medicated feed after the sulmet treatment, and I'll be getting vaccinated chicks, OR feeding medicated, next time. There just seems no other way. Our brooder is very clean, we were doing everything "right" and still this happened (actually the vet said a too-clean environment can be a problem: no chance to build up immunity!) ...... well.....They'll be eating organic by the time they're laying. I just can't go through this again!!
Sheesh. What a day. I did not get 5 minutes of work done!!!! I am ragged and exhausted!!! But-- Lillith is looking better, and I have a diagnosis and treatment. So that's all good.
Thanks for your help and support all day, folks.
Stacey