Good for you hopefully all your doing will pay off. I got some horse wrap at TSC when they had it on sale I had to cut it down the middle because it wide and I used it when my hen[chicken] had bumble foot boy is that some good wrap it stayed on for a whole week with out coming off and I'm sure...
Possible it happened before you got her, I was just thinking lots of warm water therapy too this will help her build up her muscle in her legs and help her stand and walk better. when you have her in the warm water do some massage too.
One reason I do not go to TSC during chick days I cannot...
I would it may give her more support and hold the shoe better. I seen some good reports with using the shoe. i wonder if she got stepped on and injured her leg and foot.
Do you have vet wrap? best stuff in the world because it sticks to itself. make the shoe then wrap with vet wrap. When wrapping just don't wrap too tight and cut of circulation. You can even use it for support of the leg. when one of my hens broke her leg I wrapped it with vet wrap and it healed...
Have you been on this site? https://sites.google.com/a/poultrypedia.com/poultrypedia/ there is a section on treating leg problems. Hopefully there is help for your duckling.
How old? glad to hear she is looking better today, if you've check for anything wrapped around the leg and found nothing then why not treat her to an Epsom salt water soak [nice warm water.] place the ES water in something small enough you can put the duckling in to soak but not big enough it...