When I got both my brown muscovie hens,it seemed they both had broken legs. Actually one had a broken leg,the other just had a hole in her webbing,and sympathy pains for her sister.
What I found out is that they are fast healers.
for being a bird who gets preyed on, nature makes them a fast healer. the one with the hole in her webbing healed withing a day or two,the other(we call her limpy), has a limp in her leg,but she is healthy and frisky as ever.
I am sad for you and your duckie,but the good news is: she will never be able to fly and get into trouble again! Congrats,you now have a pet duck!!