The Mediator #6 Twilight

Description :

Suze has gotten used to ghosts. She's a mediator, after all, and communicating with the dead is all in a day's work. So she certainly never expected to fall in love with one: Jesse, a nineteenth-century hottie. But when she discovers that she has the power to determine who becomes a ghost in the first place, Suze begins to freak. It means she can alter the course of history... and prevent Jesse's murder, keeping him from ever becoming a ghost - and from ever meeting Suze.