Sorry to hear about your hen! I'm also sorry to say that I don't have much experience with swelling and such, though most facial swelling, eye infections, etc. is commonly from respiratory infections. Does her face have any bad smell to it? If it does, that would almost definitely mean a respiratory infection of some sort.
Here're some proposed treatments:
1. Try applying Terramycin or Neosporin (non-painkiller kind!) to the affected area; just to take the swelling down and see if that solves the problem (other than full-out treating for a respiratory infection because that may not be the cause).
2. You can give her a small dose of water-dissolved Duramycin-10 (feed-store antibiotic); I had a hen a few years ago who's eye swelled up like that, and I just put some of this into the flock's water and it cleared up within a few days.
3. Stronger antibiotics (like Tylan50; dosage: 0.5 cc/ml per day or you can split it up to 0.25cc/ml twice a day) may help to treat the swelling (which could possibly be a respiratory infection: http://edis.ifas.ufl.edu/ps044)
Please don't try all three of these at the same time (at least not #2,3), as the high amount of antibiotics would be harmful to her.
I hope that helps somewhat, and that someone else with a bit more experience can also give their advice! The best of luck to you and your hen! :)
Edited by BeanHen - 10/9/15 at 10:28am