This could be a respiratory infection - those can be bacterial or fungal. Sometimes they get viruses, like we get colds.
A vet would be best.
If that is not an option, then look into getting some antibiotics to put in her water. A couple of drops of oil of oregano in a gallon of water might help - that is just something I thought of based on the oil's antimicrobial properties. But she may be in more critical condition than that will help with, I cannot know.
If antibiotics don't start making her better after a few days, she may have a fungal infection and would need different medicine.
That's why a vet would be a big help.
Sometimes I find useful information at Majestic Waterfowl - one of their ducks picked up a fungal lung infection last year and they have written about that in their newsletter.
