Death Cheater - The Death Cheater Series, #1

Athena Gray is strange. Dead butterflies flutter to life with just a wish, and she saved her dying grandfather by willing him to live. The only person who doesn't think she's weird is Dan, the most popular boy on Omega High School's baseball team. But who can have friends-or more-when a dark spirit shows up and stalks your every move? Dan can't understand the reason Athena acts haunted until the paranormal visitor turns to blackmail, forcing her to come clean about her gift.
Manipulated into using her power for terrible things, Athena must stand up to the darkest force she's ever encountered, before the people she cares about most get hurt.