About 2 weeks ago, my 2 yr old Cochin Barred Bantam, Harriet, started to become withdrawn spending time by herself in the coop, she also stopped laying. I instantly thought she was egg bound so I brought her into the house, put her in an Epsom salts soak for 30 minutes, gave her calcium, mixed electrolytes and probiotics into her water, made her a mash of organic oats and organic chick starter, also gave her NutriDrench. I set her up in our downstairs bath where it was nice and warm, quiet and sunny. After about a week or so of intensive round the clock care, she bounced back and was starting to act like her old self: chatty and active, or about as active as a little Cochin Bantam can be...lol. However, she never did pass an egg so after some probing, and watching her for over a week I came to the conclusion that she was not egg bound - I've lost an egg bound chicken before and her symptoms although similar were not entirely the same. So I decided to put her back with the general population. For the 1st 48 hrs back with the flock, she seemed a bit slow but otherwise ok. Then the 3rd day I noticed when she came out of the coop (very slowly) the other hens trampled her knocking her down, she made her way to a sunny spot, laid down, feathers fluffed (it was cold about 18°) and closed her eyes. Then immediately the other hens (much larger Black Australorps and Ameraucanas) went over to her and started aggressively pecking and jumping on her and she made no effort whatsoever to avoid the aggressive attacks. I rushed in, scooped her up and brought her back inside the coop where I have an isolation area set up. I put her inside it, gave her some fresh bedding, warm oatmeal mix, water with the electrolytes and closed her off from the flock - only wire separates them, but there's a private nesting box area for her. The next morning she was in dire straits! Very lethargic, pale comb and wattles, neck sunk back into her body, fluffed feathers, droopy wings and tail, eyes closed and she refused to eat or drink. So I brought her back into the farmhouse to administer round the clock care. I set her back-up in the warm and sunny downstairs bathroom. Made her a slurry of organic oatmeal, organic chick starter, organic apple sauce, organic honey, organic cinnamon and proceeded to feed her with a syringe. I also gave her the electrolyte water by syringe, and NutriDrench. I continued this supportive care for the next 3 days and she seemed to be holding her own. After researching the web, all I could find that she possibly had Blackhead Disease, so I rushed to the pet store to purchase some fish meds (metronidazole) the recommended med for Blackhead Disease. I managed to get 2 doses into her within 24 hrs but she crashed very quickly, and around 2:30am she started thrashing and screeching in her crate, woke us all up. I rushed down and she was having violent seizures, eyes closed, head bobbing, grossly dilated pupils, wings flailing, body twitching, it was just horrid! My poor sweet Harriet! This continued for about a 1/2 hour getting worse and increasing in frequency each time, we just could not stand to watch her suffer and die a slow agonizing death so we gave her peace and ended her suffering. I did manage to get video of her seizures. I then spent the rest of the night crying as I cleaned up the bathroom and washed everything down, including myself. I never did get much sleep after that. As it's -6° here this morning in the Great North Woods of Maine, I placed her back in the crate and put her out in the barn, it's Sunday so I cannot reach the State Veterinarian until Monday. I am at a total loss of what she contracted that lead to her death. I'm a bit panicked as I have 29 other chickens still in the coop and obviously I worry about a possible contagion taking out my entire flock. Has anyone on this forum had a similar experience or heard of something similar and could shed some light on this situation? I should note that she never had any blood in her poop, no discharge from her eyes, nares or beak, no respiratory distress, and her crop was good, it emptied as it should. I would like to note that I am relatively new to chickens but I have rescued and raised other animals (domestic, livestock and wild rescues). I keep my coop very clean, change and clean their water 2x day, put Bragg's Organic ACV in their water, feed Nature's Best Organic Egg Layer Feed. A feeder with just oyster shell and grit. Treats include organic rolled oats, organic scratch, dried mealworms from Uncle Jim's Worm Farm (USA worms only - no Chinese worms), organic veggies like kale, spinach and cabbage - they love the greens! And on cold frigid days/nights I supplement cracked corn. Yes my hens are spoiled, but all of my animals are spoiled, including my rescues. Any advice or words of wisdom would be most appreciated. Thank you.