I'm in the same situation with Kiwi, my green female Parrotet. She'll be 2 yrs. old on Jan. 1st and has been plucking since she was 7 months old. My other two P'lets don't pluck at all.
It started suddenly with Kiwi, she plucked her body bald in one day. I rushed her to my avian vet. He ran tests and said she was completely healthy. Gave me some baby Benadryl and Avi Soother. She started letting her feathers grow back in and then, 2 months later, she pulled them all out again.
Since then, she's plucked. About six months ago, she also barbered her tail down to nothing, and has kept it that way since then. A few weeks ago, she started on her wings. Up until the wings, she could still fly beautifully. In the past 3 days, she's pretty much finished off her wings and now, she can't fly well. She can fly, but doesn't land well.
I have tried everything, and I mean EVERYTHING over the past year and a half. Nothing has worked at all. Anything you can mention, I've tried. She'll let a few feather grow back in and then pluck them out.
I've pretty much given up any hope that she'll stop or even slow down, but the last three days have really discouraged me. I've tried just to accept the situation and ignore it, but when I see her pulling out feathers, and now she's even pulling out the down, I feel very upset. I wish I could help her.
So, yes, it is very sad and very discouraging. Oh well, thanks for reading my rant! Maybe someone will come up with a solution some day -- other than the 100 things I've tried that didn't work!