Stress can definitely make a chicken poop differently. I'd keep her under observation in a warm, dim, quiet place... like a dog crate in the garage.
I would offer her some boiled egg with vitamin water and see if that perks her up. If not, consider worming her with something like Valbazen liquid goat wormer. Her poop could indicate she has worms, which could be leaching nutrients from her.
Can you tell if she losing weight at all?
And make sure she is drinking water... It is vital that she remain hydrated... if she stops drinking, you may have to tube her water to help her get through.
MrsB