Best case scenario, she's hot or tired, maybe she's sitting in an awkward position and can't breathe properly. Maybe she's choking because she ate too fast. If that's the case, she'll be fine.
Is she rattling or wheezing? If that's the case it's probably a simple respiratory disease that can be easily treated with baytril. Remove the chick and eggs immediately, you don't want it to spread to the babies. They'll be fine in an incubator.