Put her in a quarantine coop that is warm. Mix some white sliced bread with milk and put 3 or 4 small pieces in her mouth, one at a time. Give her time to swallow each piece before placing another one in her mouth. If she wants more, let her eat it. Her poop will be somewhat runny the next day but you can start giving her a little solid food if she will eat good. Dehydration is a big problem with sick fowl. check both her ears for infection (cheese, pus, mites, lice). smell her breath for infection. A stinky breath is a sure sign of infection in the inside.Check her for mites and lice under the vent and along the feather shafts. Hopefully nothing serious like MareKs Disease. Be sure and keep water out for her to drink and keep her sitting upright and warm.