Vanishing Acts by Jodi Picoult 

Delia Hopkins has led a charmed life. Raised in rural New Hampshire by her widowed father, Andrew, she now has a young daughter, a handsome fiance, and her own search-and-rescue bloodhound, which she uses to find missing persons. But as Delia plans her wedding, she is plagued by flashbacks of a life she can’t recall. And then a policeman knocks on her door, revealing a secret that changes the world as she knows it.

In shock and confusion, Delia must sift through the truth – even when it jeopardizes her life and the lives of those she loves. What happens when you learn you are not who you thought you were? When the people you’ve loved and trusted suddenly change before your eyes?