Grounded : the adventures of Rapunzel / Megan Morrison.

Enhanced descriptions from Syndetics:

"Think you know Rapunzel's story? Think again, because the tower was only the beginning..." -- Jennifer Nielsen, New York Times bestselling author of The False Prince In all of Tyme, from the Redlands to the Grey, no one is as lucky as Rapunzel. She lives in a magic tower that obeys her every wish; she reads wonderful books starring herself as the heroine; her hair is the longest, most glorious thing in the world. And she knows this because Witch tells her so -- her beloved Witch, who protects her from evil princes, the dangerous ground under the tower, even unhappy thoughts. Rapunzel can't imagine any other life.Then a thief named Jack climbs into her room to steal one of her enchanted roses. He's the first person Rapunzel's ever met who isn't completely charmed by her (well, the first person she's met at all, really), and he is infuriating -- especially when he hints that Witch isn't telling her the whole truth. Driven by anger at Jack and her own nameless fears, Rapunzel descends to the ground for the first time, and finds a world filled with more peril than Witch promised...and more beauty, wonder, and adventure than she could have dreamed.