Should never be blood in poop. First immediate thought is coccidiosis. We lost 2 birds this summer from that. Quickly spreads. Easily treated. Easily diagnosed with stool sample. I would get on this quick. If you have the ability to take her to a knowledgeable chicken Vet, I would definitely do that. Coccidiosis will not go away on its own The weak birds will die pretty quick. If one bird has it, they all will have it. If it turns out to be Coccidiosis, it is easily treatable for the whole flock via their water.