Welcome to BYC. You have a pool for her, but do you see her using the pool often?
Pekin's, along with other heavyweights/meat duck breeds are predisposed to developing hygiene-related problems, due to their tendency to become inactive, sit around a lot, and not bathe by themselves. There appears to be a lot of mud, in the first picture, so that along with her not getting in water very frequently could cause some pretty poor feather quality. Usually, the wings are the first to become non-water repellent, then the rest of the body.
View attachment 2443649
If their pen area is muddy like that all of the time, it would be best to add some sort of absorbent material to the area to help keep it dry. I have personally found, using fine wood chips, leaves, and other decomposing matter increases absorbability in the run while maintaining a good smell.
If you aim at keeping their pen area dry, and clean as possible (hard I know), and try to figure out if there's a reason she's not bathing much, you should see some improvement in her feather quality. Ducks don't do well with ramps, so make sure she can get in, and out of the pool easily. You mention you have drakes, so make sure the drakes aren't bullying her out of the pool. Wet feather can also be set on by malnutrition, clogged oil glands, and conditions that increase the birds inactivity like Bumblefoot.
Here is some additional information on wet feather :
http://www.majesticwaterfowl.org/artwetfeather2.htm