A book that might help, since Delia enjoys cookbooks so much, is Barbara Kingsolver's Animal, Vegetable, Miracle. If you're unfamiliar with the text, it's the nonfiction story of the family's year of eating local food, mainly vegetables, mainly grown from their own farm. Each chapter is based on a particular month (or period of a few weeks) and what foods are in season, as well as some recipes written out in story form by the eldest daughter, Camille. There are some really great introductions to "fresh produce, well prepared" that clearly speaks to picky eaters -- and the "let's see if we can do it" challenge of the story might well appeal to a teenage girl. There are some very clear, direct passages that talk about raising animals on a farm for food, which may prove troubling, though.

Really, what I think might be helpful for her is the conceptual excitement of a new endeavor, relayed via a narrative story, that challenges the reader to "try something new" and offers clear descriptions and recipes to make the challenge less than frightening or overwhelming. I know that I've never been so excited about asparagus and rhubarb as I am this spring.

Good luck to you, and to Delia.