That's great! It's almost like the leg is very weak or injured, as much as the foot - just looking at the bathtub video. So a little hobbles might really help get it in proper position. But looks like good progress! Keep up the good work!
So sweet of you to take in this little one, provide a friend, and go to such lengths.
Here is a thread where someone cured their duck's curled foot using a cut up credit card and bandaids. I noticed there are also a few more threads you might look at for ideas. It's good you're helping this...