How to fix a broken mallard duck wing?

I have 4 juvinile mallard ducks that are just starting to fly and when my sister threw her favorite one in the air (its name is pepsi) she only threw it a few feet above her head so Pepsi only had a moment to open her wings, and when she did she hit the side of our garage. Her wing has broken now for 4 days but we need her to learn to fly, because the other 3 ducks won't fly south for the winter without her (I'm not too sure if they will anyways but I'm hopefull because I don't want to kill them...). I need some desparate help to heal my bird bacause we can't bring her to the vet.