My hen isn't laying, won't eat, and is weezing?

[countrychicks8]

My buff Orpington started weezing today and her breaths sound very labored. She hasn't layed an egg the past few days. She won't eat which is strange because she is my largest and often hungriest hen. The weezing really concerns me. She opens her beak wide to breath and is set apart from the other. Any ideas on how to help or what is wrong?

 

[Blackberry18]

Bronchitis, most likely. Separate the bird from flock, and find a place where you can get a vaccination. Keep on eye on the rest of the flock; bronchitis spreads rapidly.