Greetings, I am Dr. Pat. I have worked with birds for many years. I will do my best to help you. I am sorry no other expert has taken your question. We all come online at different times, I have just logged in and saw that you have not been answered. I hope I can still be of assistance.
It could be related but no necessarily an infectious cause. Other things to consider are contaminated feed, fertilizers/pesticides/garden chemicals, fumes, environmental impact.
The only real answer would come from a post-mortem exam of the deceased chicken AND any wild birds, and a thorough exam of the living bird by a poultry-experienced vet. Unfortunately the signs you describe are not specific to any one problem. A bright red comb can indicate fever, inflamation, toxins, fume inhalation; bloated (I assume you mean the abdomen was distended?) again could be from almost anything.IMPORTANT
Check the website for the feed you give, there have been many recalls.
The problem you have here is to find out what exactly is the cause. There is nothing specific in what you describe, quite literally 100 different diseases can have the same presentation. Luckily there are labs that work with small producers and an start diagnostics for a very reasonable fee.
There are so many myths in poultry medicine and diseases that I do not have the time to go into every detail, but botXXXXX XXXXXne you need facts to do right by yourself AND your birds.
The sick hen is in very serious trouble, and needs local veterinary attention. These signs are of a very sick bird, and not specific to any one disease. And that means it is not fair to you or her to guess, there are so many possibilities.You are going to need local help on this, and a scientific and solid diagnosis to find safe and effective treatment.
You can examine the bird thoroughly again, including opening the mouth and having a good look in there for mucus, redness, masses or anything else unusual. You can take the temperature gently with a rectal thermometer. Anything above 105F/40C is significant. Palpate the tummy for an egg, fluid, lumps or anything else. Check all the joints for swelling, pain, and mobility.
Move the bird indoors to an aquarium, box or carrier with soft towels or hay in the bottom, no perch, and food and water in low bowls that can be reached easily. Keep her partially covered, warm and quiet.
Do not try to force food or water. You can offer warm cooked rice, pancakes, cornbread, grapes, melon, greens in addition to normal food.
I know it is expensive, but you may not have many home options, because the first thing you need a vet for is to find out what is going on. Treatment is only as good as the diagnosis. If you call around, you may find a vet to work within your means.
She needs to see an avian/poultry-experienced veterinarian ASAP for complete examination, diagnosis and appropriate treatment. Checkhttp://chickenvet.co.uk/http://poultrykeeper.com/poultry-vets-uk/poultry-veterinary-practices-services-uk/
The expense for this is going to be a lot less than inefficient, ineffective, dangerous treatments, guesswork, and loss of the flock; not to mention possible implications to human consumption of tainted eggs. Many states/governments have poultry diagnostic labs that charge very reasonable fees to test for common diseases. In the UK, check: http://chickenvet.co.uk/lab/index.asp
If this were my patient, I would start with complete fecal analysis and direct smear, stained with Sedi-stain and unstained for multiple parasites, fungi, spirals; direct smear stained with Sedi-stain and unstained of the oral cavity; bacterial culture and sensitivity of the feces and choana. Depending on the case I might do a fungal culture. Routine blood work is necessary to rule out other issues. There are MANY DNA/RNA tests for bird diseases. Ultrasound is often more informative than radiographs and does not require anesthesia (ask your vet about this option). Generally I start them out on medications as indicated by the tests.
Pet/feed store medications and home remedies are harmful, ineffective, immuno-suppressive, and make them much worse and may interfere with the veterinarian's diagnosis and treatment. Do not use them.
The flock should be on a high quality pelleted diet with extra greens/pasturage. Overcrowding, cleanliness, proper water, environmental temperature, humidity, ventilation, photoperiod, and toxic exposures should be addressed. Check this
http://www.poultryhub.org/index.php/Welfare_of_poultry_in_periurban_environments for husbandry advice.
You need to check for fly and mosquito access, as they can carry certain diseases, and check for external parasites. Mites, lice and fleas (in some areas, ticks) can contribute to over-all health issues, anemia, and disease transmission.
Check with your local wildlife carers/rehab organizations to find out where wild birds should be submitted for postmeortem exam. Governmental agencies usually do this for no charge.