She's sick and you need to separate her from the flock asap. And you need to start her on antibiotics soon. Go to the feed store, get some injectable Tylan, and ask them how to use it. Really better to take her to a vet if you can. If neither of these options work, you can get other (oral)antibiotics, but generally you have to order them on line. keep her eating and drinking, make sure she does. Tempt her with goodies to mix in her feed like oatmeal or a few chopped berries, bananas, yogurt, meal worms, etc. Sounds like she might have coccidiosis as well. You could try getting some medicated chick starter to give her along with her other food, it has gentle meds that might help with the bloody droppings (cocci). If that doesn't work, there is stronger med for cocci, also to be found on line. She could have one or more of a number of illnesses, I'm just taking an educated guess based on the symptoms you mentioned.
List out as many symptoms as you can, including what you feed your birds, how old she is, when the symptoms started, etc. Separate her and put her in a warm dark pen where, Ideally, she can still hear her friends and maybe see them, but they won't have contact with her.
