It usually depends on how long the niacin deficiency has been going on as to how long it takes to recover. If it was left to where legs bowed before treartment there is always a chance not alot can be done or feet are severely pigeoned toed but there is always hope for legs to be strengthened No matter how long the deficiency has been, [I know this doesn't pertain to you and your duckling.] But can you get a video uploaded here so we can see how your duckling is walking and standing. Sometimes it can be genetic too or even a deformity from something happening in the bator fluctuating while being incubated. How long has it been since you upped her dose?