Right now, I see all my chickens doing that mouth breathing....I think it helps cool them off in this 80-90 degree heat. She looks healthy........Tylan should work, but I think you should only use it for 10 days. I had one chicken with a cold once.....she gurgled and sneezed (right in my face once--eww). I put her on Duramayacin (it's a weaker antibiotic) and I put her in a cage in the basement, and I also ran a vaporizer on her with vicks! I truly though she would die, but she's all better now! One of my favorite EEs.