I usually do direct dosing. The direct dose is .045 ml per pound twice a day. So for instance if she weighs five pounds, that would be about .23 ml twice a day. Usually you do that for up to five days, with three days being the minimum.
She might not have been getting enough with it in her water, since ducks tend to make a mess and who knows if she actually drank all the water or if it got splashed out, ran out of her bill while she was drinking, etc.
If she remains lethargic and droopy, it might be a good idea to do another round via direct dosing for the whole five days, and see if that perks her up.
