I am sorry for the great delay. I have been out of internet contact and only now just checked in.
Vinegar does nothing except discourage water consumption. And because of the crop situation and complicated GI in chickens, probiotics do very little either. I would rather you spend money on diagnostics and the good, targetd, and effective treatment.
It is sad and unfortunate, but the deceased bird may be quite valuable to help the rest of your flock. If you still have her reamins, and experience vet can do a simple post mortem exam and may be able to make some informed suggestions.
Having any ill birds examined is very important, and collecting droppings from ill and normal birds very important.
With warmer weather, there are many pathogens that can be active, and some that can spread by mosquitos and flies.
The odd head movemnets are very concerning, as they indicate a likely encephalitis or othe neurological disease. This can be from viral, bacterial, parasitic, fungal infections; toxins; pesticides (I assume your vegetables are not treated); hyperthermia; and many many more reasons. So you can see that doing a few tests and sorting it all out is the only way to decide what to do.
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 bot***** *****ne you need facts to do right by yourself AND your birds.
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.
For the most ill:
You can examine the birds 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 birds 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.
The bird, bowls and unit must be kept very clean.
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. Check
https://aav.site-ym.com/?page=basiccare click on "find a vet"
for members of AAV in your area.
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.
Because you have others and presumably use the eggs, it is important to have a solid diagnosis and treatment safe for egg consumption. You can check with local County Extension offices, the closest Ag university with a poultry department, or with the closest vet school for a local referral.
If these were my patients, 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. 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.
Overcrowding, cleanliness, proper water, environmental temperature, humidity, ventilation, photoperiod, and toxic exposures should be addressed. Check this
#34 for chicken husbandry advice.
Chickens: download through Zoological Education Network
(www.exoticdvm.com), or printed copies may be
requested at(###) ###-####br />
Backyard Poultry magazine
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.
They may need injectable antibiotics, calcium and many other medications. Act quickly and good luck.