That is a bummer and I am sorry about the duck. They are very tough critters. You can clean up the wounds with peroxide and then coat them with an antibiotic cream or ointment like Terramycin.
You should know that leaving ducks out over night is an invitation to disaster. They are..well..just sitting ducks. Ducks sleep on the ground and are easy prey for predators. You will need to close them up every night in a predator proof house/pen or you will lose them.
As for temperatures..ducks are cold weather creatures..they are covered with duck down. They do very well, even in sub-zero climates as long as they have a dry, clean place to sleep, deep bedding, out of the wind and with water, (unfrozen)to drink.
50 degrees is warm for a duck. Do not add heat or light. As mentioned already, do protect the duck from flies. And be sure she has water deep enough to wash out her nostrils and clean her eyes while she is recuperating. A good basic duck chow with lots of greens added will help a lot.
A wonderful source of information re ducks is Dave Holderreads book "Storey's Guide to Raising Ducks" or..."Raising the Home Duck Flock" which is the older edition and it's just as good used.
Good luck, hope all goes well. LQ