The Dragon Amulet - The Family Relics Trilogy, #3

Jasmyn has suffered more loss than she can bear, but she finds hope when she learns of her grandmother's darkest secret: magic that can reverse time itself. Along with her coven sisters, she journeys to the only place the enchantment will work-the Isle of Enid. Although Jasmyn never learned the spell, she hopes the island's supernatural forces will give her insight and help her turn back the clock.
But Jasmyn isn't the only one after this magic. Ryland, an immortal seer, devises a plan to use the spell to go back centuries to kill Finna, Jasmyn's great-grandmother, and change the fate of his people. If he succeeds, Ryland will erase Finna's bloodline from history. Jasmyn's entire family, her sole existence, is at stake, and time is running out.