The Sacrifice of Sunshine Girl - Paige McKenzie, Nancy Ohlin

Sunshine Griffith can communicate with ghosts. Even more amazing-to herself; her boyfriend, Nolan; and her adoptive mom, Kat-she's recently learned she's a luiseach, one of an ancient race of creatures who protect humans from dark spirits and help them move on to the afterlife.
Sunshine's supernatural abilities grow stronger by the day, and danger draws closer: the demon army wants Sunshine dead. Her biological mother, Helena, and the mysterious man in black, may be lying in wait. Fortunately for Sunshine, she has a lot of people (and ghosts) to protect her-including Ridgemont's mysterious new student, Sebastian. But time is running out as an unexpected event unleashes a fierce war between the luiseach and the demon army. Sunshine will soon learn a shocking truth about herself... and what sort of sacrifice is required to save the world.