Thank you both for responding!
I'm in Montana and it has been a mild Spring with some rainy days and temps around 85 high.
They free-range in a large, suburban yard and their coops are clean. I use Timothy hay and pine shavings for bedding (in case any of that is relevant.)
Do you think her immune system might be down from the stress of raccoons? Is there a respiratory disease that can come up due to stress?
Last month, I programmed a new chicken door incorrectly and we lost 2 chickens. Last night, the racoon was back. He didn't get in, but they were all very distressed about it and this morning is when she showed this symptom.
For now, I'm going to quarantine her and monitor the situation. I will be able to see better how she's eating, drinking, and pooping.
How do I know if I'm dealing with Gapeworm or Respiratory infection? Can I treat both simultaneously?