I didn't even know that she was really ill! She was in the nest box at night instead of on the perch. I checked for any mass (like a stuck egg) and found none. she didn't seem to be suffering, but how could I tell? I made myself a note to check on her this morning and she was cold on the floor. How can I find out what killed her? I don't want all my other chickens to die from the same thing.