It's been a calm month, but things were going too well and of course something had to happen. This morning when I opened their coop (roughly 30 mins ago), one of the chickens was making a gargling noise when breathing and when trying to make sounds. She doesn't move too much, but when I try to pick her up she still runs away. She didn't eat or drink, at least not while I was there. I noticed some sort of discharge around her nostrils. It's clear and kinda sticky, but this might be because it started drying. The poop inside the coop looks normal. Pretty cold outside too, around freezing temperature for the past 2 weeks. Today I will install a heat source. This is one of the oldest, 8, almost 9 months old. I'll give her antibiotics today. What can it be and what do you suggest?