Empire of Blood - The Rebel Empire duology, #1

Lilly Faine is tired of classmates dissing her family, and doesn't care when she receives suspension for nearly punching the lights out of a classmate. Her father isn't crazy, even if he does spout stories about a world full of magic, a cruel king who hunted him, and has a shattered amulet that tingles when Lilly touches it. When an old enemy appears under Chicago's beloved Bean, Lilly and her brother Gabriel are shoved into the impossible world their father believed in.
Alone on opposite ends of a war, they race to rescue each other. Lilly finds aid and friendship in a band of rebels, but she is also hunted by the emperor's personal assassin. Gabriel gains the help of the emperor, but Gabriel's choices to do good may lead him into dark shadows he can't find his way out of. Magic thrums within their reach, promising aid, and Lilly and Gabriel both must decide if the magic they seek - and the causes for which they now fight - is worth the risk of their souls.