The TRYLLE trilogy (SWITCHED, TORN, ASCEND) by Amanda Hocking is only available as eBooks at this time, but due to the series' success, they will be published in book form in the near future.
Wendy is a high school girl who never quite fit in. When she is nearly kidnapped, she discovers that she was swapped by Trylles, or Trolls, to live as a human in place of a baby that they took back to their secret kingdom. Her human mother never believed that she was the right child, and her Trylle mother is cold & distant. When Wendy is forced to live in the Trylle kingdom, she finds out that she is a Trylle princess, destined to be the queen. Adapting to this strange life is difficult, but eventually she finds her powers and a new strength. Recommended - 3 Elves