Ok thank you very much! I've cleaned her foot up and gave her a pad of cotton wool on the bottom of it to relieve stress, (these lot literally go wherever they please so I expect she went somewhere she shouldn't have). She seems a lot brighter now and I've put her in a kennel full of clean straw with food and water. I actually hatched these lot during lockdown so I'm not super informed on ducks, what is the best for vitamin B supplements? In the water or in her feed?
If you are in the UK (?) the easiest vitamin B supplement to get would be some nutritional yeast, and sprinkle about one or two tablespoons over her feed.