Book I of the Bound by Blood Series....
High Priestess of her bloodlines, Samanthra Lampir is on the verge of her Awakening, something every Vii before her has welcomed with ease. Not Samanthra though, for her Awakening is prophesied to bring about the doom of her and those she loves the most, her sisters. In secret, she undergoes dangerous rituals despite the fatal threats of TERAH and the rising strengths of its enemies. That is, until the night a great storm of unknowable power releases a prophecy, a revelation, that will change her world--the world of TERAH-- forever.
One of my favorite series.