P. C. Cast 
Divine by Blood 

Eighteen-year-old Morrigan has always felt different, like she didn’t belong in small-town Oklahoma where she grew up. But on an outing with her friends to the deep, gem-filled Alabaster caves, Morrigan discovers that she’s much more than just different, she’s magical.When she learns the dark truth about her ancestry from her grandparents, a devastating accident transports grief-stricken Morrigan to Partholon and into the keep of the Sidetha, where she is regarded as the Light Bringer, the Goddess Adsagsona’s Chosen One. Luckily for her, many strangely familiar priestesses and otherworldly beings are there to offer her guidance in her new world, including a brazen, handsome centaur High Shaman named Kegan.As she tries to make sense of the powers swirling inside her-and confront her growing feelings for Kegan-she must fight against the lurking darkness that threatens to permeate her very soul.