I just noticed my hen has a swelling on one side of her face, around her eye. What made me notice was the fact that i thought her eye looked odd, on closer inspection her eye seems fine, just the swelling round her face making her eye look smaller. She is puffed up slightly and not moving around a lot. From what i can tell, she is keeping that eye shut quite a bit. There is no other symptoms and all my other chickens appear to be ok. She is a 2 year old production red. Not sure why or how this has happened, but i will add that she is one of the roo's favourites and her and her sister have been plucking each others faces the last few months. When i just went out there now to check her, she fought me when i picked her up, normally she is fine with me picking her up. What can i do and how can i treat?