One of my chickens sounds congested. She has no discharge to speak of but I can hear a rattle when she breathes. She shakes her head every now and again like she is trying to clear something out. Her comb is still bright but she has not laid in over a week. She is the only one I have noticed this with but she is in a run with 9 other hens. Any ideas? Should I separate her out or is it too late all the others have what she has?