Lightning, the White Stallion 1986 one on netflix

When a stolen white stallion escapes his captors, young Stephanie Ward gives him a new home and a new name: Lightning. As she grooms the horse for show-jumping competition, the pair forms an unbreakable bond. But when Stephanie finds herself in need of an expensive operation, and Lightning’s original owner tracks him down, Stephanie sets all her hopes on first prize at the Nationals – and on the horse who’s become her best friend!