What are you feeding her? My first thought is niacin deficiency which is common in ducks on chick starter crumbles without a high vit B supplement. You need durvet high level vit B compound. It's a liquid that we give orally to ducks. At 2 weeks old, your duck can have 1ml a day soaked into a few mealworms or crumbles: stay and watch it eat the full dose. If it throws around some of the mealworms and you can't be sure it ate it all, give a second dose later in the day. Continue the high level vit B for at least a week after cessation of symptoms
If you cannot get durvet high level vit B compound from your feed store immediately, order on line from Amazom and buy a human Vit B 3, niacin, preparation from a pharmacy. Be sure the Vit B3 is flushable (no flush no good) and not long acting. Use that until the durvet arrives.
Also change the duckling onto duck feed with good levels of niacin. I just got a bag of Dumor duck crumbles 22% protein and extra niacin for two ducklings I am caring for. But add nutritional yeast 1tablespoon per cup of crumbles. The cheapest source of nutritional yeast is Walmart own brand. I would continue added nutritional yeast until your duck is fully feathered and possibly up to 12 weeks. My son has his laying Pekins on brewers yeast year round but I don't use it for my flock of adult drakes. Just my rescued ducklings
Let us know how you get on