Sky Horses: Eye of the Storm by Linda Chapman
Erin had always believed in magic, but she never believed she had powers of her own! Until one day Erin looks up into the clouds and sees a herd of magic horses! Erin discovers that she is a weather weaver with magical powers, and the sky horses need her help. Erin's powers have grown strong and now she faces her greatest challenge yet - freeing the sky kingdom from the dark cloud horse's rule. But, even worse, possibly having to say goodbye to her new sky horse friends forever!