Brighid's Quest by P.C. CAST

Rather than follow her family's restrictive rules, centaur Brighid chose to set out on her own to make friends and form relationships with humans as well as centaurs.

Now she's facing her toughest challenge yet. While helping guide home a grieving human –– Cuchulainn, her friend Elphame's brother –– Brighid finds herself beginning to care for him. An emotion forbidden by her clan.

To add to her troubles, the Great Goddess has awoken the power of the Shaman within Brighid –– the first centaur so blessed in ages. And just as she's torn between taking up a power she never expected and a love she's afraid to admit to, Brighid receives a vision of a tragedy that might destroy everyone she's ever cared about…