Once upon a time, when Lauren Horowitz was a little girl growing up in Atherton, her "absolute favorite thing to do" was to have her parents drop her at Kepler's Books in Menlo Park, where she says she would "sit in the stacks for like four hours reading books."

She loved Kepler's so much that one year she had her mom convince Kepler's to sponsor her Menlo-Atherton Softball League team. "I was such a little book nerd," she says, she wore her Kepler's emblazoned uniform everywhere.

On March 6, in what she calls a "childhood dream," Ms. Horowitz returns to Kepler's, to read from and sign her own novel.

"Shattered Blue," a fantasy novel filled with poems by its young heroine, was published by Skyscape, Amazon's young adult imprint, in September. It is Ms. Horowitz's first published novel, but she has been a Hollywood screenwriter since soon after graduating from college.

She has written television movies and pilots for networks such as The CW and ABC Family (which recently changed its name to Freeform), writing mostly for young adult audiences.

Ms. Horowitz, who turns 33 on March 9, says she always wanted to be a writer. Proof of that was found recently when her mother, Lenore Horowitz, was cleaning out the family's garage. She and Lauren's father, Dr. Lawrence Horowitz, still live in Atherton. Lauren says there were 11 books in the garage she had written in Mrs. Martin's third-grade class at Las Lomitas School.

It was her fourth-grade teacher, Nancy Lund, who really convinced her she would be a writer, she says.

Ms. Lund allowed the class to visit the La Entrada computer lab every Friday to "just write whatever we wanted," Ms. Horowitz says. "I ended up writing my first novel." The plot included girls and horse camp, she remembers.

Lauren went on to Menlo School for middle school and high school, and then to Harvard, graduating in 2006 with a degree in English literature.

Arriving at Harvard, her only school where her three older siblings hadn't attended, "I had this kind of transformational moment," she says. "I thought, I'm really going to write my own story now." That included giving herself a new name, Bird.

"It was very important to me to choose my own name when I was stepping into my own world for the first time," she says. "I believe very much in the power of words and language to not only name reality but to alter reality."

She's been known as Bird ever since, although she writes for television as Lauren Horowitz.

Her current project is a pilot for "Familia," based on a real Bay Area Latino family with "tremendous kids who really lift themselves up," including a son on the U.S. national soccer team, she says.

The idea for her novel "Shattered Blue" came to her during one of the seasonal breaks that come with television writing.

"I was wondering why we don't see very many heroines in novels who are writers or poets," she says. "In high school I was ... what I would call a secret writer," she says, not showing the poems she wrote to anyone.

"I thought, what if there was this girl who was growing up and she processed the world through her writing, the way I very much did when I was that age?" She envisioned the girl finding a hidden magic world within her real world, one just as fantastic as her imagination.

She decided to try putting those ideas into a novel, even though she knew nothing about novel writing and had no publishing contacts.

Three months later, "Shattered Blue" was finished. She asked the head of The CW Network, where she was doing a writing project at the time, for publishing advice, and the manuscript was passed on to Amazon's Skyscape, which published it.

While Hollywood may sound romantic, it often isn't, says Ms. Horowitz, who splits her time between Kauai and Hollywood. Writers come up with the ideas, the plots and the characters. Then, however, "there are so many people involved, who come into the project and supersede you creatively," she says. "At times it can feel like there are very many cooks in the kitchen, and the final project can end up a little bit muddled."

Screenwriting, she says, "is a very intensely collaborative situation, which in and of itself isn't bad, except as a writer you're the absolutely lowest on the totem pole."

"Now that I've gotten a taste for writing novels, and the absolute freedom it gives the writer, and the fact that the writer gets the final say in content ... I never want to go back," Ms. Horowitz says.

"Shattered Blue" is the first in a trilogy, she says. She has completed the second book and is working on the third.

Her writing routine includes walking on Kauai's beaches with her rescue dog Ninja and recording her thoughts for the book, then returning home to write them down.

"I'm a huge fan of very intricate plotting and plot twists," she says

So it turns out that there's a happy ending to this story. The little girl who said she always "knew I was going to be a writer," is exactly that.