The extra benefits of nutritional yeast is the niacin. It also has a lot of other B vitamins in it as well. Brewers yeast works as well, but doesn't have the nutrient concentration that nutritional yeast does. It doesn't matter overmuch for your chickens, but a lot of people have had issues with...
I'd get some nutritional yeast and add that to her diet to boost niacin as well. Flock Raiser doesn't usually have enough niacin for ducks, and niacin deficiency can cause leg issues.