In 27 Days (Watty Award Winner 2012)

Hadley Jamison doesn't know what to think when she hears that her classmate, Archer Morales, committed suicide. She didn't exactly know him, but that doesn't stop her from feeling like there was something she could have done to help him.
So to Hadley's surprise, on the very night of Archer's funeral, she has a run in with Death himself and is offered the chance to go back in time to stop Archer from ending his life. The catch? She only has twenty-seven days to do it. And if Hadley doesn't succeed? Well, she doesn't want to think about that.