Is she drinking any water? If her crop still feels full, but you don't think she's eaten anything today, then you might consider she has an impacted or "sour" crop. There's quite a number of threads on BYC about that, just type "impacted crop" or "sour crop" in the search box.
I her crop is not full, eliminate that possibility and move on to checking to see if she is "egg bound." Search for that term for lots of good advice on how to diagnose it and how to treat.
Like I said, you need to do a little more investigation to try and narrow down the large number of possible ailments. In the meantime, go to the grocery store and purchase a bottle of Pedialyte and give that to her instead of plain water. It contains both sugar for energy, electrolytes, and will help keep her hydrated. Feed her only "soft" foods like yogurt, boiled or scrambled egg chopped fine, baby cereal made with Pedialyte or plain water. If you decide to try antibiotics, Aerosmith99 suggested starting her on Tylan 50. It may not help, but it won't hurt her either.
Post again if you come up with anymore symptoms/clues.