do you feed enough cut greens and fruit, insect, mineral powder for babys and the right feed for them ? do they have a heat lamp and enough water ...i would take her away from the other for protection, keep her watered and feed and warm under high enough heat lamp or those baby chicken heating table thingens..
and when possible ask the vet as soon as possible or go there today...sometimes it is a little thing, like that she is still to young or needs more food and keeper more warm and away from being hurt by larger chicken^^
how is her temp, the beak, nose holes, eyes, the feather and skin...her legs? when she is chirping like crazy and goes calm when you take her into the Hands, maybe she misses her mother and is to young to be away from her, or is cold.
you maybe could put a soft towel loose around her so she can put head onto it...not sure...i think i did see this somewhere in bird Forum...vet can say if this helps.
the vet can help you bether, give them a call.^^
hope all goes well.