Guardian Legacy, book 1: AwakenedEdnah Walters2010

Most teens turn sixteen and get the license to drive, but Lil Falcon gets the license to kill demons. Orphaned as a child and raised by an eccentric grandfather, Lil is concerned with surviving high school and is unaware that she's a Guardian-a being with super powers charged with killing demons and protecting humanity. When she meets Bran, a mysterious boy with amazing abilities, his psi energy unlocks her latent powers. But Bran has a secret that can ruin their growing relationship, and the truth she discovers may destroy everything she believes in unless she finds the right balance between love and sacrifice.