Greetings, I am Dr. Pat. I have worked with birds for many years. I will do my best to help you.
That is an unfortunate and common problem in cockatoos. They are at the same time wild animals, and feathered people. Their medical issues are quite complex. So there will be no easy answer nor quick fix. You will have to work at all levels to solve and treat this problem--psychological, behaviorally, medically, welfare/well being.
Tell me how she is kept:
Housing--cage or no? Material on bottom of cage?
Toys/playtime human interaction?
How long part of your family?
Change in the home/family/circumstances?
Has she gotten into anything or is she ever unsupervised?
Harassment by pets/children/guests?
Where are you in the UK?
Feather issues can be caused by a multitude of things, including bacterial skin infection, viruses, fungal infections, allergies, metal poisoning, hormonal flux, psychological or combination of these factors. The difficulty is diagnosing the problems and assigning an intelligent treatment plan. Your vet will want to run a number of tests so that appropriate medications can be prescribed.
Inflammatory skin/follicle disease is common. The causes can include local infection, metabolic problems, or even intestinal parasites. It can also be a prime area for even more serious problems like skin cancer. An avian-experienced vet should take a look at the poor bird, and run some tests. If he were my patient, I would start with complete fecal analysis and direct smear, bacterial culture and sensitivity of the feces, skin, feather pulp, and choana. Depending on the case I might do a fungal culture. Routine blood work is necessary to rule out other issues. Generally I start them out on injectable antibiotics and an anti-inflammatory such as ibuprofen.
may need to seek behavioral counseling IN PERSON, family members and bird. There are some very serious issues developing here, and the family reactions are important. This is not an easy set of problems to correct, and the humans are mainly at fault and therefore the ones in need of behavior modification. I always have the entire family plus bird come in for at least an hour-long consult; it is much easier to do in person and evaluate everyone's non-verbal relationships. So online I can only give general suggestions and urge that you seek proper consult at home. There are a number of people who do this, but you may have to call around and check with a number of avian-experienced vets to find a reputable behavior person.
Online you can check to see if this https://companionparrotonline.com/beak_book_detail.html
is available; it has some practical solutions to common behavioral problems. There are a number of "Idiots Guide to..." books and the parrot or cockatiels do have some good insights.
This bird msy hsve been coddled and fussed over as a baby, and now she has become spoiled. Of course this gains bad attention, so the cycle worsens. He is approaching puberty, and the fussed-over baby is now confused over whether she is offspring, mate, or rival. Parrots are flock animals and are NEVER alone in the wild, and their friends, siblings, parents and other adults do not tolerate bad behavior. In a loving human family, she does not have that variety of input. It is natural that a bird be anxious about being alone. Se needs to learn to entertain himself and to have more self-esteem. That means you are going to have to give her even more attention, but in a different way than in the past.
First the bird needs to have a complete check up and health screen. There may actually be a real physical self-damage.
Then strict 12-14 hours DARK QUIET UNINTERRUPTED SLEEP AT NIGHT. Sleep deprivation leads to bad behavior, anxiety and physical problems.
The bird needs proper diet.
She needs something to do with his mind. You can read children's books to her, point out the pictures, show him garden catalogs, teach him to count, anything to make her educated. She may be bored and needs to learn to play by herself with the assurance that he has not been left out or left behind.
Talk to her like an 8 year old kid. Be consistent, not afraid, gently assertive, and NO DRAMA. Did I mention NO DRAMA?
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. Homeopathy and natureopathic techniques do not work in avians and can actually be very dangerous.
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. I really must stress that you need a bird-experienced person, and not just a vet who advertises that they care for birds.
You need to take your bird to see an avian-experienced veterinarian ASAP for complete examination, diagnosis and appropriate treatment. Check
for members of AAV in your area or call your regular vet and see who they recommend; ask if they really have worked with birds a lot. Unfortunately, this list does not rate competency or experience, but is only a starting place; the vets at least take the avian medicine journal and hopefully see a bird or two a year. The best referrals are word-of-mouth, so check with several non-bird vets, the humane society, parrot rescue groups, bird clubs, etc. for their input. As you might guess there may be controversy and varying opinions even with this. Even board-certified avian specialists may not have a lot of practical bird experience. Unfortunately there are few resources available to refer you to really good, clinically-experienced bird vets.
Here are a few suggestions that I give everyone: important!
The following guidelines help with basic issues such as nutrition, obesity, good immune status. Surprising how the following can make a bird healthy, and how infrequently birds are ill if they are on the following regimen. No amount of medicine is going to work if the birds' basic needs are not met.
AAV recommended lab work
Birds should be on a high-quality, preferably prescription, pelleted diet: I prefer High-potency Harrison's
In addition, they should be offered dark leafy greens, cooked sweet potatoes, yams, squash, pumpkin; entire (tops and bottoms) fresh carrots and so forth. No seeds (and that means a mix, or millet, or sprays, etc. etc.) and only healthy, low-fat high fiber people food. A dietary change should be closely monitored and supervised by your avian vet.
Birds should get 12-14 hours dark, quiet, uninterrupted sleep at night. Any less and they can suffer from sleep deprivation and associated illnesses. They should be covered or their cage placed in a dark room that is not used after they go to bed.
The cage material should be cleaned everyday, and twice a day if the bird is really messy. Paper towels, newspaper, bath towels are ok. Never use corn cob, sawdust, wood chips, or walnut shell.
Food and water dishes should be cleaned and changed daily. Keep one set cleaned while the other is in use.
Fresh, perishable food should be placed in separate food bowls. Remove fresh food from the cage after a couple of hours to avoid spoilage.
Change cage papers daily, and clean the grate and tray weekly.
Clean food debris or droppings from toys and perches as needed (which can be as often as once a day).
Grit is not necessary for birds, and will cause digestive problems and death. The best sources of minerals (and vitamins) are leafy greens. Never give grit, gravel sandpaper or cement perches. A bird will eat those to excess when it is not feeling well or if there is a nutritional deficiency. They do not need it at all (an old myth from the poultry days, even poultry do not need it). It can cause an impaction and lead to serious or fatal consequences.