I have a ten year old female ringneck parrot. Last year she had lead poisoning and plucked out most of her feathers. Almost all her feathers have grown back now, but there are still areas on her chest and back where she only has down feathers and none of her normal feathers. Will these feathers ever grow back?
If the feather follicles are damaged in certain areas, then it's impossible for the feathers to grow back. Your bird will not have any luck in having all feathers again. I would recommend taking your bird to the vet to stop your bird from further plucking her feathers.
According to this article at backyardchickens.com:
If the feather follicles are damaged or in the case of repeated feather loss, like plucking, the feather won't grow back. Diet can also be a factor as well as advanced age.