One of my chickens seems to have trouble breathing!!

[Kianaslair]

She is about 3 months old, is eating and drinking but I noticed this morning that she is taking deep breaths out of her mouth. She is the only one out of 9 chickens (6 Wyandotte, 2 Golden sex links, and her) breathing this way. I am feeding them the last of this medicated chick feed, Start and Grow. They run free on 2 acres for most of the day with my 2 goats, unless it is really windy and rainy as it was today. I am very new to raising chickens. Can anyone tell me what this might be, how I can help her, and if it could be life threatening? I am so worried about her. She has always been my favorite and I lost the other like her as a chick to cocci. I don't know what kind she is, I was told Wyandotte from the person I got them from but she doesn't look like the others. Also she will stand with her head drawn in and close her eyes. Am I just being a worried newbie?