I'm happy to hear you found a vet.
Generally, the major cause of lameness in waterfowl is due to a deficiency in niacin (B3), since you're not seeing much improvement with the B complex, it seems the problem is not related to niacin, although, with a bird this age, improvement may take several...
For some odd reason, I never got the notification you replied back after my post. How is she doing, were you able to take her to a vet? If not, I may be able to suggest a few things.
Thanks for providing us with additional information.
In regards to what might have caused her leg problems, I would have to agree with you that it's injury-related due to the sudden onset.
This is nothing uncommon in ducks, especially with heavier weight breeds like Pekins. While ducks are...
I'm very sorry to hear about your duck @Fabfur . To let us help YOU, could you provide us with some additional information regarding the bird?
How old is she? What is she being fed? Do you have any pictures of her setup? Have you picked her up and inspected her legs to ensure they bend at the...