Destiny With Death by Judith Post

Loralei has always been able to see the dead who stayed behind when they died. But when Loralei takes Death for a lover, she develops the gift of being able to call a spirit back to Earth after they have left this realm. Now she is able to communicate with spirits to help families find the bodies of long-dead and missing loved ones. But when a grieving mother and father ask her to locate their daughter, Mandy, Loralei gets more than just a body. Mandy's battered body is lying beside another girl's, and when the police dig up both girls' remains, their killer knows someone tipped them off. The killer learns about Loralei and her gift—a gift that can point the police in his direction. He's killed before. He can kill again, but Death has no intentions of losing Loralei.