Flicka (2006) on Netflix

Rob McLaughlin runs his Rockies horse ranch with a firm hand. That includes grooming gentle, smart, mundane son Howard as his successor, without bothering to find out that's the boy's daily nightmare, while he dreams of a writing career. Howard's sassy sister Katy was send off to a boarding school the family can ill afford. During a holiday, she discovers an even more free-spirited wild mustang and decides to tame it, hoping it may help to convince pa she's fit for ranching. Trouble comes from nature, kin and others.