What to do with a feather-picker...?

[MyLittleRedCoop]

I have 4 Australorps, all aged 7 1/2 months old. We live in MN.

I have 2 girls with messed up tails and some minor feather loss on their tummies.
Then, I have one poor gal who looks like she's been through the wringer. Her head is bare, her tail is all shredded, her butt is bare, her tummy is bare... She is a pitiful sight, indeed.
And then I have one who looks absolutely perfect, with not a single feather missing or out of place. Hmmm... who could the culprit be?

I feel like I should be removing someone from the coop, but I'm waffling on who...
If I bring in the miserable girl, so she can grow her feathers back, and prevent injury, will the bully start in on the next lowest in the pecking order?
If I bring in the bully, I'm concerned that the poor little gal will freeze.
Thoughts on who I should bring in?

Just as an FYI -
Stuff I've Tried:
* I put some stuff (Rooster Booster) on the really beaten-up one, that makes the skin darker and less prone to picking. But she was missing even more feathers on her head this morning. She doesn't have any open wounds yet, thank Heaven!
* I tried adding interest/toys to the coop for them to peck at.
* They get treats to peck at daily. (eg: meal worms, lettuce, apples)
* I have a flock block in there for them.
* I also added some high-protein conditioner to their food, to increase protein levels and help grow feathers back. Nothing is helping.
* I tried to put a sweater on the one who was half bare. She wiggled right out of it. And, of course, her neck and tail were still sticking out.

Further details:
* I know it isn't molting because it started on the tails, not the head.
* The feather-picking started in January, when we moved them into their permanent, larger coop. The coop is 10x12, and they literally have 12x more room in it than they did in the old one. They also have a 300 sq ft attached run.
* At the time they moved to the larger coop, there was a HUGE temp dive (highs in the negative digits for over a week), so they were confined to the coop. As soon as temps were normal again, they were able to go out.
* Pinless Peepers are on their way, and I'm hoping they help. But will they have to wear these forever?

Any other suggestions or solutions I might have missed?

 

[azygous]

Always remove the bully feather picker if possible. If you remove the victim, she'll have an even worse time of it when she returns. Taking the trouble maker out of the flock for awhile may change behavior, or not, but it will be hard for her to come back into the pecking order at her previous rank in the pecking order because it will have changed while she's been away.

Pinless peepers may help if you get them on early in the feather picker's career. But I've had two feather pickers learn to pick feathers in spite of wearing the peepers.

 

[MyLittleRedCoop]

Well, the stinker is in the laundry room.
But I feel badly for the half-naked gal in the coop. It's cold out there!
Now that you say it, though, it makes good sense to take out the bully and not the victim.
I posted this in Emergencies, too, and was told to boost protein, which I had, but I will take it another step up.
I'm hoping this works... Thanks for the help!