Yes put the brewers yeast over their feed daily just make sure it has adequate niacin or switch to Nutritional yeast. 1 tab over each cup of feed.
You sound experienced with giving liquid by mouth but I still feel I need to share...
That is so awesome!! Congrats on having it all go so good. Just gives you a warm feeling to see them be so accepting. To Runners the more the merrier. lol
Beautiful ducks :love
She is adorable; love the name Hazel too. As for not floating most likely, it's going to take a while for her to get her feathers where they should be by swimming and preening and spreading the oils from her preen gland over her feathers to make them waterproof. She may need to molt too so if...
Poor little one so glad you rescued her. I guess you could slather some bag balm on her feet but it will make them slippery so she need to be kept on something so her legs don't slip. Was she the only duck? Hopefully good care feed and time she'll be right as rain. How old?