One of my layers has been on the nest for a couple of days and didn't want to leave the coop to go outside. I thought just broody or starting to molt, because a lot of feathers are missing on her underside. Then, yesterday, she came off the nest inside the coop, and the others started attacking her, as if to kill her. So, I got her separated - no apparent physical injuries. I set up a pen in the garage where it's cooler to better observe her. While I was setting it up, she had a big poop (all diarrhea with a small patch of blood, and some hard white porous bits, about raisin-size, that wouldn't dissolve under the hose). After that, she pooped a couple more times and they became progressively more watery. The first poop was really foul smelling. Concerned that she could have necrotic enteritis, I started her on tetracyline, which is the only antibiotic I could get locally and quick. Also gave vitamin/electrolyte mix. Both are in her water. She seems to have drank about a cup of water in about 20 hours. She's bedded down, and not moving much. I did get her to eat a few layer pellets, and some cracked corn, but not much. I only have four birds, others are fine. I have had problems with thin shells, but started adding oyster shell to their food, and that got better lately. Prior to that, we occasionally got broken eggs, which they quickly cannabalized, but I wasn't sure which chickens were laying the thin shells. Also had some shells which were very rough textured, but none lately. I would be grateful for any advice. Thanks.