Could it be possible that when she is in the water her webbed toes are not opened up like a flipper and she is trying to tread water like a dog? That is kind of what it looked like to me when I watched your video clip again.
Oh my gosh I couldn't live there. lol. 
Yes a little different for sure, hopefully with a little more swim time all will be fine, please keep us posted. I watch our two oldest Mallard hens and how they use their little flippers in the water to maneuver and it's amazing how quickly they can change direction.
