Almost guaranteed it is either worms or Coccidiosis. If your vet will do a fecal float for you, you will know where to start. They aren't very expensive; here they're around 18.00 here, and don't let the vet say they won't do it because they're not a bird vet, because poop is poop, and the parasites are basically the same. If you don't have the resource to do that, both deworming and treating with Amprol (Corid) are safe to do without a fecal float, and will not hurt her (although I always do one at a time if I'm going to do both). Some birds are very susceptible to coccidiosis even though their flock mates may not be, especially young birds. As they get older, they should develop a sort of immunity to it. So, here's the question. Have you ever treated them for coccidiosis (and that includes feeding them medicated chick starter, or using Corid?) Or, have you ever dewormed them? If the answer to both questions is "no", then if I were you I'd start with the Corid; it's easy to use, 2 tsp per gallon in drinking water, and mix fresh every day, for five to seven days. If it's Coccidiosis, you should see a very quick improvement after you start the Corid. Treat the flock too, even if they're not showing symptoms. If you've done this before, then try deworming (if you haven't) with a broad spectrum dewormer There are several on the market including Safeguard (which is popular and easy to find). Just make sure you get a broad spectrum dewormer, and not one just for roundworms. Make sure you start RIGHT NOW with something, because birds can deteriorate very quickly, and they tend to conceal symptoms until they are very ill. It's good that she's eating and drinking; do everything possible to make sure she continues to. She can eat whatever she likes. Also, if you treat her for worms, treat the flock, too.
