HELP! Duck with mite like symptoms!!!

I don't know Buck, but usually if a duck has swimming water they very seldom get parasites. here is a link on what to look for though scroll down and you'll see pics. does she sleep inside a duck house. go in of an evening and stick your hand down in the bedding if there are mites they will get on you. lice are easy to see they are usually on the feathers around the vent.
http://anrcatalog.ucdavis.edu/pdf/8162.pdf

 

I may be a bit slow, but she looks like she's had some feathers pulled, maybe, I know sometimes Hazel looks a little like that and then Bean gets some extra time out to give her a break.

 

If she does have mites spray her down with citric acid like lemon juice. Just mist over the feathers and she should spread it with her bill. I do that with my chickens and peafowl never ducks since it's rare for them to get something like this since they are almost always near water 24/7