Hello...
I have whats known as a 'clipper' which is what it sounds like you actually have. She doesn't PLUCK her feathers, but she clips them in half... here's some pictures of her from when I first got her:
(sorry about the size, I had to redownload it to photobucket)
Currently she is fully feathered. I found she does it mostly in the fall.. seasonally. And this past fall was a LOT less than the previous fall/winter/spring.
On top of that, I had a GCC. (I miss her dearly.)
The fresh food diet really helped her stop plucking. After that, its a matter of finding her toys that keep her entertained. She's a very picky bird. So, those piniatas you can buy, and softer wood toys that she can just demolish are in constant supply at my house. I leave the wood/string at the bottom of the cage for her to work at also (she likes to untie the rope that holds the wood onto the main part of the toy.)
Pie tins for baths while I'm running the vacuum-cleaner helps. when I'm vacuming, she has to be bathing.
Pumpkin seeds in an easy to figure out foraging toy is another thing to do.. it keeps Quana busy for hours.. (although, now with Lacey here, minutes.. )
I found, at least in my case, the change in her envoronment, change in cages, and all around change helped. You can find her story somewhere down below in the ekkie section. I can't promise the pictures are still up though.. Her cage was horrible, she had no perches... Her toy was a metal chain with a bell. I didn't blame her in the slightest for clipping.
Edit: A picture of her after living with me for a while, and her new cage:
