could be exposure to dusts...
I've been hearing some chickens have shown a sensitivity to pine shavings..but it's rare..
what all do you feed?
describe the droppings in detail..color and consistency..
you can take her to a vet if you're able to..if not..
any feed/farm/livestock supply store carries antibiotics...
here is a link to online source; click antibiotics in the side board..click meds for what they are used for..
most will be available at feed stores..in the LIVESTOCK section.
http://www.firststatevetsupply.com/store/
I prefer Tylan 50 injectable..also comes as water soluble (goes in drinking water)..
but she might just need something like a tetracycline..(shown as oxytetracycline)
some people use Duramycin..
is she wheezing? have any mucus? wet or swollen eyes?
best to bring them in so she can keep warm and no draft or wet or chilling....then let them gradually get used to cooler temps.(after she's better)
another thought..
check the crop..do you know how to do that?
she might be eating the bedding...
feel the crop for grainy feeling, or doughy mass or lump..best to check in the morning before she eats.