Loreena's Gift by Colleen M. Story

Where do we go when we die? Loreena knows. She's been there, and it's not at all like her uncle, a reverend at a small-town church, thinks it is.
Loreena Picket is a blind young woman who lives with her uncle, a reverend at a small-town church. Loreena has a strange gift, which she's not really sure is a gift at all. Her uncle has made good use of it, involving her in end-of-life “ceremonies," during which she helps terminally ill people die in the most humane of ways. Taking their hands, she kills them with an invisible, painless power, but not before traveling with them to the other side. The payoff? On her journey to the afterlife with her companion, she can see.
Loreena's uncle believes her power is a gift from God, but when Loreena's troubled brother returns to town, she saves his life by killing a drug dealer who isn't ill at all. Thrown deeper into her brother's dark world and forced to survive being kidnapped and used for her power, she begins to wonder: Is she angel of mercy, or evil assassin?