Maryjeanash thank you for sharing the videos -- they are very helpful for us to understand what is going on
I think your duck seems to be improving on how she was on May 17. Her issue is chronic leg problems from long term lack of niacin and probably protein in her diet, and you are doing the right things now:
Durvet 1ml per day on a treat [for example mealsworms] so that you can watch her eat it.
Brewers yeast on her food: sprinkle on1 tablespoon on every cup of duck food
Feeding duck pellets: shie needs one cupful in the morning and one cupful later in the day -- leave any uneaten where she can return and help herself when she wants to.
It will take time -- could be months -- for her to get stronger again. Letting her exercise as much as possible in water is really important. It's ducky physiotherapy! The water takes the weight off her leg joints and allows them to move. She was moving both legs in the pool in your video.
I think that your "babying" her is good -- help her in and out of the pool as you don't want her to get an injury on top of her chronic leg problems.
It's good that she has an attentive drake that she wants to be near and he wants to be with her. Be sure that he doesn't start over mating her. And discourage him from mating out of the pool. Its better for her legs that he only mates with her in the pool.
We will be here for you long term as you nurse your girl back to good health and stronger legs!!