Sorry to hear about your duck.
What brand of brewer’s yeast are you feeding her? At what dose? Could you post a video of the duck trying to walk? To post video you’ll need to upload it a video platform like Yotube or Vimeo, then copy/paste the link here. Could you feel up and down her legs, and look for swelling, signs of discoloration, or warm spots? How do her footpads look? What kind of area is she being kept in during the day?