I think if you can keep her in a "hospital crate" where it is relatively clean, with fresh bedding, water, good food, that's half the battle.
The colloidal silver is a good idea. Some folks do well treating such wounds with a simple mild saline solution four times a day at first. There is a product called Vetericyn that also reduces risk of infection. I would not cover it tightly, as I believe it needs some air to avoid gangrene.
You can consider oral antibiotics, but she may not need them. It's a tough call, as it is difficult to detect systemic infection in a duck till it's well along.
I don't know your weather, but flies will lay eggs in open wounds, so keep her in, away from flies. Trim the feathers short around the edges of the wound for ease of care and monitoring.
Ducks can recover from horrid injury, by the way. The vet may be able to give you some anti-inflammatory medicine that reduces pain.
Check under her wings and around her vent also for puncture wounds.
I would give her electrolytes and vitamins in water for a few days.
@casportpony has experience with medicines.
Feel free to post over on the Duck Forum if you have not yet.