Before I Wake (Soul Screamers, #6) by Rachel Vincent

I died on a Thursday-killed by a monster intent on stealing my soul. The good news? He didn't get it. The bad news? Turns out not even death will get you out of high school...  Covering up her own murder was one thing, but faking life is much harder than Kaylee Cavanaugh expected. After weeks spent "recovering," she's back in school, fighting to stay visible to the human world, struggling to fit in with her friends and planning time alone with her new reaper boyfriend. But to earn her keep in the human world, Kaylee must reclaim stolen souls, and when her first assignment brings her face-to-face with an old foe, she knows the game has changed. Her immortal status won't keep her safe. And this time Kaylee isn't just gambling with her own life...