I agree that I would try to help the duck myself at home with splinting. I would keep her inside a crate or pen with food and water for some time to limit her activity. It can take 3-5 weeks for a bone to heal.
Here is a splinting manual for birds, and the bone you are treating is on page 23:
https://theiwrc.org/wp-content/uploads/2011/05/Duerr_Splinting_Manual_2010.pdf
These are Telfa pads, and do not stick to wounds. They can be cut to fit the size needed...
That is one of the better places for a break to happen in poultry, since it can be splinted. Do you have splinting supplies or any antibiotics? I would try and see the vet if possible since it is a compound fracture and the bone can become infected. How I would treat it is to clean the open skin...