Oppression (Children of the Gods #1) by Jessica Therrien

Elyse knows what it means to keep a secret. She's been keeping secrets her whole life. Two, actually. First, that she ages five times slower than the average person, so that while she looks eighteen years old, she's closer to eighty. Second, that her blood has a mysterious power to heal. For Elyse, these things don't make her special. They make life dangerous. After the death of her parents, she's been careful to keep her secret as closely guarded as possible. Now, only one other person in the world knows about her age and ability. Or so she thinks. Elyse is not the only one keeping secrets. There are others like her all over the world, descendants of the very people the Greeks considered gods. She is one of them, and they have been waiting for her for a long time. Among so many of her kind, she should not be very remarkable--except for the prophecy. Some believe she will put an end to traditions, safeguarded by violence, which have oppressed her people for centuries. Others are determined to keep her from doing just that. But for Elyse, the game is just beginning--and she's not entirely willing to play by their rules.