Rae Carson grew up reading fantasy, but as time passed, the genre conventions that once resonated began to feel, well, conventional. When she sat down to write her own fantasy novel, she says, “I wanted to subvert those tropes and focus on what a princess is not versus the tropes of what she is. I wanted an epic quest like Lord of the Rings, but less Aragorn and more Ugly Betty.”

This idea provided the impetus for The Girl of Fire and Thorns (Greenwillow, Sept.), a book filled with her favorite elements—quests, a hardy band of adventuring heroes who play off each other, and a coming of age story—but all centered around a plus-size princess who is far from stereotypical. Carson drew the inspiration from her post-college stint in the working world, especially her run-ins with body image problems, demeaning roadblocks at work, and a boyfriend far too involved in her eating and exercise habits.

“I knew I had to write a story about a girl whose potential and accomplishments no one sees until she loses some weight,” she says. “I was hyper-aware of this being a risky thing. My goal was to show that her character growth and potential were separate from her weight, even though there were, in reality, people who devalued her. It’s hard to look past weight—I wanted to write about a girl who had value regardless of what she looked like.”

Though she’d never finished a novel before—she’d abandoned a lot of writing that she got bored with, outgrew, or felt was weak—this time it was different. “After the first chapter it had captured me so much that I knew I could finish it.” Her unusual heroine, the decidedly not beautiful Princess Elisa, is an emotional eater with low self-esteem who sits around waiting for her destiny. She is dismissed and patronized until the outbreak of war gives her the opportunity to leverage her smarts and let her inner self shine, transforming her into a major force in the conflict.

Carson’s first agent aimed for the adult market despite the author’s intending the book as YA. The manuscript failed to find a home, and Carson shelved it. Persuaded to try again when she saw that YA fantasy books with strong female heroines were starting to find a wide audience, Carson found a new agent. “Holly Root [of the Waxman Literary Agency] loved it but knew the manuscript had been out and wanted to see more to know that we could be a team, not just for this book, but for me as an author.” Carson had confirmation that she’d made the right connections when, in spring 2010, Greenwillow came back with an offer just 24 hours after being approached.

Carson’s biggest surprise in the publishing process? “How much of my job has ended up being not writing. I had no idea how much work went into interviews, online presence, editing, page proofs, talking to my publisher/agent/publicist, answering e-mail. Some days are crazy.”

Carson has been writing full-time since 2004, when she decided it was “try or bust.” She finds that her most productive times are late in the evening until near dawn. That’s when the house she shares in Ohio with her husband, author C.C. Finlay, and two teen stepsons, goes quiet and it’s just Carson and her two rescue cats.

Having finished The Crown of Embers, the second book of her Fire and Thorns trilogy, Carson is currently revising it while writing book three, The Bitter Kingdom. She laid out the whole story several years ago and has not had to make major changes in her original plans. “I don’t plot with huge detail,” she says, “just big moments and important elements, and then I have a structure but can fly by the seat of my pants when I write. The first and second books have threads that lead into the third, and that’s definitely going to be even more action-packed and exciting.”

Carson knows there’s plenty of room yet in the offerings for younger readers, but as a fan of genre classics like Dune and Star Wars, her heart knows the direction she’d like to see: “We need more stories about princesses who kick ass and farm boys who go off on adventures.”