separate the bantam...bantams are fragile when young cause of their size (all I raise is bantams)
Once you put her in a separate pen , see if she walks. How is she sitting?
are her legs paralyzed like? can you make her stand?
any cold symptoms, fluid in chest, wheezing?
How is her poop?
She may just be scared or may not be getting the food cause of the others.
Give her polyvsol (without iron). Take the dropper and run it along her beak line until she swallows. Do this for 2-3 days.
Give her some wet mash, and make her some scrambled eggs and add 2 tablespoons of buttermilk.
You can also put a CLEAN stuffed animal in her cage to keep her company while she is alone.
Pics or more information would be very helpful
good luck,
--laura--