And Now for Something Completely Different ...Sure, it's from a few years ago, and you have to buy it used (sometimes for not much more than the shipping cost), but have you read this book?
Sunshine Rider: The First Vegetarian Western
I would recommend this coming-of-age fiction western for older teens and adults. Perhaps a mature 13-year-old, but no one younger. It would be a fantastic gift for your newly-decided high school vegetarian. But, don't think it's just for kids, even though it's listed under "young adult," it's a great read for adults too. (And you don't have to be vegetarian to enjoy it, although you may decide to try it afterwards.) Each chapter begins with a recipe, none of which I've ever tried, so I can't tell you if they are good. (Note: some are meat recipes intended to disgust the reader.)
So, give this book a try. And, no, the sequel mentioned at the back was never published, so don't bother looking for it.