Looks like she's picked up an infection.
With light wheezing and lethargy, I'd say it's gone systemic and she needs oral or injectable antibiotics. I am not an expert on which antibiotics to use - but there are people more familiar with these things.
Please post over on the duck forum http://www.backyardchickens.com/f/42/ducks
More duck people are available there.
I think I have read aureomycin is an antibiotic used for respiratory problems. And in the meantime, some cooled oregano tea in the water might help - I have read that is used in poultry to help avoid the need for antibiotics.
But at this point, I think a good duck vet would be great if that's possible, and I would be deciding which antibiotic to use if that's not possible.
I would also start rinsing her eyes with mild saline solution three times a day, and putting poultry vitamins in her drinking water.
Ducks can hide illness till it's really far along, so she needs help a.s.a.p.