Hi, there!

Welcome to BackYard Chickens!
I'm sorry to hear your duckling is having problems, it'd be very helpful if you could answer a few of my questions. Where did you acquire her, what is she being fed, has she had any damage to the head or neck area recently, could she have been in contact with anything toxic, are the other duckling's showing symptoms, what dosage have you been giving the E, B, and selenium at, how often, how long, and how are you administering it?
Wry Neck is not a disease, but rather a symptom of many diseases, such as viral, bacterial, malnutrition, neurological, toxin ingestion, and few more. The point is without testing done by an avian vet finding the sole cause of her problems solely relying on anamnesis and physical examination will prove fairly ineffective in most cases. Rapid recovery after a dose of vitamin's is a diagnosis that the bird was malnourished, but since your's isn't showing any improvements it makes me think it's possibly neurological damage, as most likely by now the other duckling would's be showing similar symptoms if it were bacterial or viral.
I think an avian vet would be your best course of action, they may be able to perform advanced supportive therapy, as well as perform diagnostic testing such as CBC, Biochemistries, specific test ‘s for detecting levels of toxins, radiographs, electroencephalograms, electromyograms, auditory evoke potentials, CT scans, and MRI. These tests can be used to make a more confident diagnosis of the nature of your ducklings problem.