I am new to raising chickens; I received 25 in late April, and the were vaccinated against Mareks, and coccidosis. They get 16% layer pellets, along with a few handfuls of scratch daily. 1) Apache Girl is a 6 month old chicken --unknown breed, she hasn't started laying yet. She is perhaps 2 - 2.5 pounds 2) I noted that she wasn't interested in food on Sunday night, and again on Monday, staying by herself in the yard with a drooping tail. She is usually incredibly lively, but I was able to easily catch her to quarantine her. Her comb appears pale. Her respiratory rate is gone up from 28/min yesterday to 36/minute. Her eyes are clear, no discharge from her ears. She looks like she has some pin feathers on her head, but no bald spots, I checked her for mites and found none. 3) When I checked her over, I found no signs of bleeding, injury, broken bones or other sign of trauma. 4) I have 24 other girls who all appear fine, weather has been cooler in the evenings, but still in the 80s during the day. No rain over the past several days. 5) She doesn't want much food. I mixed some yogurt and her pellets and she took some of that along with some water, but really not much. I offered it again every 2 hours or so yesterday. Today, she is even less interested in taking in food/water. 6) She had an initial poop after I feed her yesterday, which was quite watery and green with some mucous. She had two more stools yesterday each a little more firm than the last, but still green. Today, she sounded a little congested--wheezing, but that seems to have cleared. 7) I brought her into the kitchen yesterday, and besides offereing yogurt mixed with pellets and yogurt mixed with rice along with some water, I have just been watching her. She is very calm -- normally would be pacing the cage, but she just lays there. 8 ) I would like to treat her myself , but I also don't want to infect my other birds if she is contagious. I can go into the next town to a Tractor Supply for supplies--I think they carry antibiotics if that is what you suggest. 9) She is in a coop at night and is in 20x60 pen during the day. I initally wanted them to free range, but they started roosting in trees so I had to pen them. Suggestions?