Hello and welcome to the forums, first off. A lot of the time, pigs that have never had vegetables before, including young pigs, will not eat them at first. It's simply because they aren't used to them. Persistence is the key. Keep at it. I would suggest starting with a leafy green, like romaine leaves, or a smaller treat, like carrots. Just keep offering the veggies, from your hand, in the cage, and during floor time. Leave them out for a pretty good amount of time, especially in the cage. If she gets hungry or curious enough, she'll eat them! Sooner or later, I'm sure she'll learn to love them!
You do have a point with the cavy friend thing. Cavies are herd animals and need a companion. You should see if there are any other female cavies in your area to adopt from a shelter or rescue. This will let Vanilla lead a much happier and healthier life. Maybe she'll even learn new things from the new pig, like trying new veggies!
Anyways, good luck, and see you around the forums!