I don't know for sure, but I would do a search in the emergencies section. I think there are some diseases that start with a swollen face/eye. Hopefully it's just a bee sting and she'll be fine in a day or 2.
I had a hen get pecked on the eyelid and it was swollen like that. It doesn't really look diseased. I'd give it a few days and if the swelling doesn't go down, seek more information. I know how it feels when a hen gets hurt. They are really very vulnerable, aren't they? Good luck!