Heart to Heart book by Lurlene McDaniel

From Lurlene McDaniel, the bestselling author of young adult inspirational fiction, comes Heart to Heart . This emotionally charged novel explores loss, love, renewal, and the ways in which these complex bonds within families and between friends are tested at life's most challenging moments.
 
Elowyn Eden and Kassey Messechek are best friends. They share every aspect of their lives. But one thing Elowyn has not yet shared with Kassey is that she checked the organ donor box on her newly acquired driver's license. Kassey only learns of this in a startling and devastating way—when Elowyn's life-giving donor wishes are about to be honored.
 
Arabeth St. Clair has not had the luck to have a best friend. Due to her diseased heart, she's led a sheltered life. When Arabeth is sixteen, she and her mother receive the call that will change their lives—but they don't know to whom they should be forever grateful.
 
When the worlds of these three girls and their families intersect, lives are changed in ways never imagined. Most especially, it is Kassey who sees things differently, for she can keep alive the memory of her dear friend by sharing the renewed life of another teenage girl, while helping to ease the pain of the two families involved and coming to terms with her own.