I wouldn't be concerned about the temperature. (Look at how many wild birds sleep outside in all weather.)
But I would worry about a predator getting her.
Usually, I would say to just make sure she goes into the coop in the evening before roosting time, and shut her (and the others) in. But depending on how mean the bully is, that may not be a good choice here.
How big is the coop?
Can you arrange to have two or three roosts, so the bully can sleep on one and not be able to reach birds on the other one?
Is there any way to divide the coop, or have a second coop?
A few possibilities for actually getting her out of the tree:
--if she's low enough to reach, just grab her after dark and put her in the coop for the night.
--if she's too high to reach, go out while it's still light, take a long stick, and gently push/herd her off her branch. Keep bugging her until she finally flies out of the tree. (Doesn't work after dark, because she won't want to fly when she cannot see.)
It looks like you have been a member of BYC since May 14, 2006!!! That is a LONG time.
I see you are already receiving suggestions regarding your chickens in a tree.
In the future, you may have better luck with responses with different issues in a different section than this one that is for "New Member Introduction".
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