Hi Gill,
Sorry to hear you're having a few probs with your ex batt hen. Hens stop laying when they have their annual moult, so that is normal for this time of year. You have helped her by giving her extra vitamins, but she will still need them to help her feather re-growth. If she is pecking at herself, anti-peck spray or wound spray is a good idea.
Also, have you checked her for lice? These are greyish in colour and just visable to the naked eye. They tend to accumulate mainly around the vent area where you may also see white powdery clumps attached to the base of feathers - these are the eggs. Lice tend also to affect birds more who are elderly or 'under the weather'. To treat these you can buy a powder from your local pet store. Your Veterinary Surgeon may be able to suggest something stronger in a bad case. If you see lice on her, it is worth checking your other birds too.
I hope your girl sill soon be on the mend.
All the best.