The White Pony.

Leah is eager to visit her uncle's ranch in Ireland, until her attempt to ride her cold cousin Shannon's horse results in Silky being injured and she is ordered not to ride again. When she meets Lucky, a leprechaun who only communicates with her, she learns that the beautiful white beast she's glimpsed from afar is in fact a bewitched fairy Sorica, who needs help retrieving a magical horn to return to her true form and her own world. Now Leah must juggle secretly helping Lucky, whose reasons for helping might not just be out of kindness; putting up with Shannon; and trying to win Uncle Jaques' trust by entering her newfound "horse" in the local race.