I have some 4 week old Black Stars and some 6 week old Isa Browns in together, and one of the Isa Browns seems like she has stopped growing or is at least way behind. She seemed really weak for a couple of days, so I separated her for a while to guarantee her access to food and water and to monitor her. She's eating and pooping fine now. She is smaller than the younger chicks, has no interest in flying. Today I put her back in the brooder and she moved around a bit but seemed timid. I'm worried I'll need to keep separating her to make sure she's eating and drinking.
Is there anything to do help her catch up?