I can't help much with a broken leg. I recommend going, but I know you said you don't have the money for it. The only thing I would recommend is just keeping the duck still and calm and maybe giving her some calcium and seeing if it goes away to see if she can walk again. Especially after you...
If you see a callus or scab, soak it with Epsom salt to soften the scab or callus, then you can carefully remove it with a sharp scalpel, and then you can add drawing salve and wrap it.
I just checked, and they were three days old when I got them.
Maybe it is how I took the picture, although they are pretty much fully feathered from tail to head; I might say they are 5 inches.