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's being injured, and her 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 legendary unicorn Uafus, who needs help retrieving her horn to return to her own world. Now Leah has to juggle secretly helping Lucky, whose reasons for helping may not just to be out of kindliness, putting up with Shannon, and trying to win Uncle Jaques' trust by entering her newfound "horse" in the local race. - IMDb