Greetings, I am Dr. Pat. I have worked with birds for many years. I will do my best to help you.
A photo would be very helpful.
Please do not use any more of those products, they are actually quite irritating to bird skin and can cause more harm than good. The only safe thing to use is warm water and very mild, diluted dish detergent with thorough rinse and dry.
The most likely thing is lice egg deposits. They can appear in quite thick mats.
Fly eggs also can appear this way. There are a number of dermatitis and skin infections that can cause a scaly appearance to feather shafts and skin.
Nutritional issues can also cause odd skin and feathers.
The best answer is to take an affected bird and the feathers to a knowlegeable poultry vet and have the material identified under the microscope, properly. Then an appropriate treatment plan can be drawn up.
Lice are faily easily treated by OTC poultry lice products or any flea powder labelled safe for pupies and kittens. Best application is to each bird, but you can also mix it into the dust of their favorite dust bath area.
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.
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.http://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.aspx
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 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. I Overcrowding, cleanliness, proper water, environmental temperature, humidity, ventilation, photoperiod, and toxic exposures should be addressed.