I use Epernix pour on on all my fowl including my ducks and goose. I only do it it the middle of winter when swimming water is just about nil. If they have swimming water year round I'd say unless they were living in nasty conditions they wouldn't need to be treated. This will take care of External and internal parasites
If you decide to treat let me know and I give you dosage unless you already have it. go by size of bird.
Call duck hen probably weighs what about 1lb or less? I have dosages for chickens but use it to get the dosage for my ducks like Lf chickens get 5 drops my goose gets 10 my Muscovy girls get 6 and my drakes 8 my bantam chickens get 3 drops my standard chickens get 4 if your call is around a pound then I'd say 3 drops. What i like about the Epernix is it is safe to continue to eat the eggs after using instead of having to toss then. If you think these dosages are not to your liking then maybe you can google it and find out. I have been using these dosages for almost 3 years and have never had a problem.
(Busily taking notes, here)
Okay now you need to address the eye issue, I believe along with treating for mites and other internal parasites I'd do something for her eye, terrimycim eye ointment or silver or even Vetericyn can be applied around the eyes Like Amiga said if she hasn't had water deep enough to wash her whole head she may have picked up an infection of fungus.
