I know you're looking for the short answer - and it is that Vitamin C will not harm anything since it is naturally occuring in your body already - unless you feel any kind of irritation and then I suggest a diluted solution.
The long answer is that if you better understand the natural workings of your own body it is easier to identify homeopathic treatments that may help and why western medicine's approach isn't working anymore (if it ever did). This specific blog entry is a powerpoint presentation by a doctor for other doctors and it explains the vaginal ecosystem and the existence of BV better than I could. It also makes it easier to understand any kind of imbalance such as yeast infections, etc.