My 2 year old RIR hen is breathing with her mouth wide open, wheezing. She seems to have difficulty drawing in enough air. Her comb is drooping and looks dull and darker. ( that can be lack of oxygen though, right?) I noticed it last night and removed her from the flock. I started her on an antibiotic in her food and gave her fresh water with some gatorade. Her crop is completelly empty. She was the same this morning. I checked all of the other chickens last night and again this morning, listening for wheezing and looking for darker combs and everyone else seems ok. So far. Any idea? I don't know what else to do for her. I feel so bad. You can tell how bad she feels.