Swollen eye and side of head

[Amp]

We just returned home from vacation this evening to find one of our girls was sick. My Dad has been caring for them for the past week and separated her out this past week when he noticed she was not coming out of the coop and sitting in a corner. He couldn't see anything obvious until about 3 days ago. I've inspected her and can't find anything obvious. Her poop is fine, no running nose or other signs of respiratory illness. She is eating pellets and drinking water. They have not been out to free range since we were leaving so she hasn't gotten into anything. She is about 4 years old and had recently stopped laying in the last several months. I dusted her for mites just in case I was missing something. I have Penn G and BioMycin on hand, just not sure which one to try. Thanks.

 

[Amp]

I will add that her comb is very pale and she is obviously not feeling well at all, she is just laying in the back of the crate.