I found one of my ~2 year old hens this morning in a nesting box with what looks to me like a swollen and much redder than usual face. She is not sneezing, wheezing, there is no discharge from her nasals or her eyes. But her face is pretty swollen. I immediately isolated her and cleaned the coop, and none of the other girls seem to show symptoms. She has normal stools and laid a nice egg today. It's been rainy here the last few days (Southern California), so I suppose that could have something to do with it I just really hate to jump straight to antibiotics since their overuse leads to resistance, especially with no other symptoms. Though I will if need be. The closest match of a diagnosis I can think of is infectious coryza.
The feed store was out of straw and shavings last week so I had to get a bale of Timothy hay, it seems if she was allergic it would have appeared earlier though since it's been in the coop for at least a week.
Does anyone have any insight on what this may be (her face is a bit greasy because I applied a little VetRx) ?
one of her BM's: