Hugs to you both. Ducks can recover from awful injuries. Tub time is a good idea.
A good duck vet is best. Meanwhile and in any case,
Ckip the feathers around the wounds. clip them to about half an inch long, so you can see and treat. Look under wings and around vent for puncture wounds.
The duck is likely in shock, and may not want to eat for a day. Just be sure there is plenty of fresh water. I would add vitamins and electrolytes to the water twice a week.
Rinse the wounds three times a day with saline solution. Keep the duck in, away from flies - they will lay eggs in the wounds. I would look into setting up a sling.That keeps weight off the injured leg. Leave it open in back to avoid holding feces against the body. Leg may not be broken could be muscle injury, let's hope for the best.
Talk to the duck, I would move the duck to a "hospital" shelter, with another, buddy duck for company. Has the dog issue been dealt with? You do not want a repeat performance.
