Betrayed (Guardian Legacy) - Ednah Walters

Lil isn't just an average teenager. She's one of the Nephilim--the descendants
of humans and angels--which gives her some serious psi skills and a mission for
redemption. Just when Lil thinks she's found a balance between her normal life
with human friends and her training to become a Guardian, she's warned that
someone close to her will betray her. When the boy she loves starts acting
strangely and one of her human friends acquires a supernatural ability, Lil
begins to realize that someone is manipulating the people she loves... and won't
stop until she's been lured to the dark side.