So sorry for your duck. I have tried plain yogurt on my animals who feel sick and I swear it works. Yogurt is a natural antibiotic. My ducks LOVE peas, lettuce, watermellon, cantalope, and grapes. I would try a small bowl of mixed ingredients mentioned here with a tbl. spoon of yogurt as a glaze. I don't know if your duck will eat it but it's worth a try.bMy ducks will eat human food over their crumbles any day so it usually works. I would also try spraying your ducks face with a squirt bottle....just mist her face and mabey it will clear out her nasal passages some.
I hope she gets well. You might also want to bring her indoors and fix a small box with a few towells and let her rest indoors as apposed to being around the other ducks. She may need some alone time to cope...It may also really help with the feeding issues since she will not have other animals bothering her. I housed my pekin indoors for two months after her foot surgery. I filled the bath tub 1/2 way with cool water and she swam and floated in the tub for hours.
I wish you the best of luck. Animals are amazing with the natural ability to heal. I have had numerous animals near death and they just bounced back on their own...Gods way of helping us out...Thanks.