I have four lovely little bantam hens. Best wishes to Maggie - keep us updated. SUdden of sporadic mortality, listlessness, green or yellow Diarrhea with pasting of the vent feathers, lost of appetite, increased of thirst, and pale.
Diarrhea sometimes occurs.
They come out at night and suck the blood of chickens. If she was broody and in her nest they could have done a job on her. Look around for little red bugs near the nest. Go at dark with a flashlight. If it is them you can dust her and the coop.