First thing I always check with a sick hen is for egg binding. This will have them fluffed up, a bit of diarrhea and looking poorly over all. Put on a latex glove with some KY Jelly or Vaseline on the index finger and go straight back into the vent. If she has stuck egg, it will be right there. Any further back than 2 inches and she is not egg bound. (egg would then still be in the uterus getting the shell on). If she is egg bound, you will want to jump on this quick. Get her soaking in warm water in your sink for 15 mins. Get some human calcium into her too. Tums will work as well. Break the pieces up and put them in raisins or some sort of berry. You can check out my article on Egg Binding in my signature for more help with this.
If she is not egg bound she could be wormy. Has she been eating and drinking ok lately? And have you wormed your birds recently? If not, you might get all of them wormed. Worms eat all the food that a bird consumes, the bird looses weight, becomes thin, gets diarrhea, the worms multiply to huge proportions and kills the bird. I like to use Safeguard Liquid Goat Wormer. You can also use the Safeguard Equine Paste. Either of these can be purchased at most feed stores and even Walmart.
If you have wormed and don't suspect them, then you might consider she has Coccidiosis. Get some Corid in the water for 5 to 7 days. You can get this stuff at most feed stores. Cocci will have them all fluffed up, standing up, weak, not eating or drinking and sometimes blood in the poop but not always.
Keep us posted!
