Separating out a 4 week old aggressive chick

Not sure if this should be in this forum or "Managing your Flock."

I got 3 GBJ (The Monsters) at the beginning of the month. A week later 3 BO's and 3 EE's (The Babies).  We didn't put them together b/c they were 2 weeks apart in age AND SO much bigger than the babies.  We would introduce them here or there, but only for short times, and always supervised.

I noticed the tail feathers were not as full on one of our GBJ's (Leela.)  The other two kept getting longer and longer feathers, but Leela's stayed short.  We've figured out that Oreo, the biggest GBJ, has been pulling them out!

Due to my allergies, the chicks had to go outside. I found a GIANT dog crate on Craigslist and used hardwire cloth to make it safe for the birds.  We put them ALL together last night.  We had separated Oreo out for the last two days and thought that maybe she'd calm down. Nope.  My husband noticed today that she had hearded the OB's and EE's into a corner away from the food, and every time they tried to go for it, she would peak at them.  So he took her out and put her in this rabbit cage we have.  The other two GBJ's don't pick on the Babies, but they don't really mix with them much.  Maybe that will just take time.

I just don't know what to do with Oreo.  I know that chickens are social, so I don't want to make her crazy by keeping her away from the others, but clearly she can't play nice.  I noticed the tail feathers on Ryan (GBJ) are kinda scraggly and not as full as Oreo's.  I think Oreo was pulling her tail feathers too, just not as much as Leela's. 

Oreo is only about 4 weeks old, so I'm really at a loss as to what to do with her. 

And I'm only saying "Her" because there's a 90% chance they all are hens.  Maybe Oreo's a roo?? IDK.  Too early to tell.  Any advice would be appreciated. Thanks!

Now they have a lot of space.  Oreo even had plenty in my previous set up, and she's the only one showing this kind of aggression.  The other two were eating with the Babies just fine yesterday  after Oreo was taken out.

My husband tried putting the cage she's in next to the brooder the others or in, but he said Oreo was just going bezerk trying to get INTO the other cage.  When I got home I took her out to pet her and stuff and she jumped out of my hands and ran over to the brooder and was peaking at it trying to get in.  She would only calm down if she couldn't hear or see them anymore.  Maybe if we left her next to them longer she'd calm down, but I'm afraid she'll hurt herself before she stops.  But she's been with Leela and Ryan since we picked her up from the feed store and has been terrorizing them this whole time.  So IDK....

We've had Oreo separated since Monday night now.  S/he is a MUCH calmer bird!  Still think it's too early to put her with the others, but s/he is MUCH better now. We'll give it a couple more days, then see what happens.  The others are getting a long just fine.

Well, Oreo has certainly calmed down.  She has no problem coming out of her cage an me holding her.  The others totally freak out. I think that has more to do with my husband and I are the only socialization she's getting while the others have each other.  I was thinking of putting her back in with the others, but they've all grown so much that they don't have enough room in the brooder for all 9.  Hoping to get the coup and run built by next week so we can put them out there.  I can't believe how fast they've grown!!