zachdave - where did you get her from? If you purchased her from a pet store then A) she probably doesnt know what vegetables are and B) she is probably sick as most petstore pigs are.
I would certainly recommend taking her to a reputable exotic vet, and also keep persisting with the veggies. It is unnecessary to feed any pig extra vitamin c unless they are sick or not getting veggies. Keep providing a variety of veggies, but until she does start eating them (and the vet has ruled out any medical problems) then supplementing with vitamin c is fine. It doesnt matter where you get the vitamin c from so long as it is plain vitamin c. Watch how much you give her as well.
aaronmeister - unless there is a medical problem with your pigs then there is no point giving them extra vitamin c regardless of their age. They should get all the vitamin c they need from their veggies. Also I believe that it is possible to overfeed vitamin c (ly knows more about this than me,
!).