At three days, it, and the others need to be taken out of the incubator.
Please remove it, and set it in a brooder with a warm section near (85/90F).
After it has acclimated, try offering some mashed scrambled eggs; if she refuses to eat, get your hands on a poultry vitamin and drip a small drop along her bill.
Administering too many fluids at once will cause aspiration, so be very careful to give small amounts at a time.
A feed and water dish should of course be provided/ given that the duckling is not stable I would make sure the water source is shallow enough it can't drown.