Ducklings can be delicate (some more than others), sometimes if they are handled right after eating/drinking this can happen. Hopefully this is all it is. I would leave her be for awhile. Check on her frequently, but don't pick her up. Take a video if you can. Update us and let us know if this continues or if she seems to settle back down. If you are able to share a photo of the brooder (maybe from above) so we can see where the heat is, and your food, water, and bedding containers/setups that would be great.
What kind of bedding is in the brooder?
What is your heat source?
What kind of container is the water in?
Has she eaten anything other than pellets/crumbles?
Is there grit available?
Can you better explain what happens when she tries to walk? Do her legs shake? Does she fall over? Does she go backwards or in circles or anything else unusual?