Why does she need her appetite increased? Has she been unwell lately?
The most natural way to increase an appetite is to warm their food, it increases the smell and makes it more appetizing.
In all my years of breeding I have never had to use vitamin supplements etc, so I know nothing about them sorry, I always prefer to do it a natural way. Try changing her food, they do get bored with the same thing.
And please peoplez, don't write in to have a go at me, I am only trying to help with my opinion, as you probably will with yours.