Hi Josephine,
I'm sorry I didn't see your question sooner. I apologize for the delay.
When a parrot sits with feathers fluffed up, it is a sign of illness. Your cockatoo needs to see a certified avian vet right away. You can find a vet near you at http://www.aav.org/.
No one could possibly diagnose what is causing the illness online. The vet will do some testing to determine exactly what is making your parrot sick and give you the correct treatment. Please don't try over the counter or pet shop treatments since they seldom work and often harm the bird further and delay effective treatment.
Please get her to a vet today. While locating a vet and waiting to go there, keep her warm -- as close to 85 degrees as possible -- and calm and quiet. Give her whatever she will eat and be sure she is drinking to prevent dehydration.
Since parrots hide signs of illness, by the time they show any symptoms, they are usually quite sick. So it is URGENT she get immediate vet care by an avian vet.
I'm providing a few links for you on supportive care and general care. Please do not use this to attempt to postpone care from an avian vet! It is urgent or you might love your beautiful goffin.
If I can help further, please use "reply" after accepting this answer.
Emergency Home care: http://www.avianweb.com/birdsafetytips.html
Household Hazards: http://www.parrotparrot.com/birdhealth/alerts.htm and http://www.birdsafe.com/
Safe and Toxic Woods: http://www.birdsafe.com/woods.htm
Cockatoo Diet: http://www.avianweb.com/cockatoodiet.htm
Signs of Illness: http://www.birdsnways.com/wisdom/ww14ev.htm
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