It would be suprising if all those breeds at the same time developed weak legs due to a niacin deficiency. Mazuri is a high quality food. Could it possibly be something else? Did it start around the time you moved them outside...even if they are afraid of things flying overhead, they might be...
Does she have access to daily fresh swimming water? That would be very important for ducks feather health! She will eventually molt and then can grow in better feathers.
Completely shell-less or do they have a paper thin shell or membrane? How is she doing today? Eating, active? If she has shown no improvement you should consider your vet euthanizing her. It might be best not to have her suffer :( Sounds like she may have a reproductive issue. It's so hard, but...
That looks painful. Do you keep it bandaged with a gauze pad? I would use this epsom salt solution linked below and re-bandage it every day with a fresh application, keeping her feet dry - taking it off occasionally to give her time to swim in clean water. Try that for a week and see if it looks...
I'm just curious as to whether they stay in hutches all the time or are allowed to forage on grass? I adopted two from a breeder who was keeping them in hutches. Mine now forage with my standard size flock and they love it!