So sorry to hear about your beautiful hen! I also just lost a real nice red sexlink today with almost the identical symptoms. I am baffled to say the least.
For the past week mine would just stand alone........while rest were free ranging..........humped up, tail and head down. She would perk up if I threw some bread and eat maybe a piece of that. I started making her a scrambled egg with yougart and oatmeal each nite and for a few nites she ate it quite well. Last nite she barely touched it and I could tell she was getting worse. Found her dead in the coop this morning.
Her crop felt fine, her vent was clean and I could not detect any lumps like egg bound, her breathing was also fine and her feathers were beautiful not scruffy looking at all, had definetly lost weight tho?????? I have not wormed my hens and this one was almost 2 years old...........could it be worms?
I am also afraid the rest of my hens could do something similar. I would like to worm them but kinda hate to right now as I finally found a good buyer for my eggs. I would rather wait till end of summer when they molt. Should I be worried about the rest of my flock who all seem totally fine, could this have just been something that only affected this one hen??