Sorry about your sick pullet. Do you have any pictures of her? Can you do a thorough exam on her when she is resting this evening? Usually when they are roosting, you can pick them off and check them over. Feel of her crop to see if there is any food in it. It should feel full at bedtime and be mostly empty by morning. If it feels full and hard or puffy in the early morning, she may have a crop disorder. Look around her vent and under for evidence of lice or mites. Check her droppings and describe them. It could be almost anything wrong, but right now with summer heat, heatstroke and dehydration might be a problem.
If she is hunched or puffed up, lethargic, not eating, and having runny poops with mucus or blood, she could have coccidiosis. That is treated with Corid from your feed store. Worms or intestinal infection, poisoning, or other problems might be possible. Is she holding her tail up normally or down? She could possibly be eggbound with her first egg, so you can easily insert a finger 1-2 inches inside her vent to feel for an egg. Wear a disposable glove if you have one, and it should feel soft. If you have electrolytes to put into her water or can feed some Pedialye or Gatorade, that would be good. Let us know what you find.
