The Return of October (1948)

Terry Ramsey (Terry Moore) and her uncle Willie (James Gleason) share a great love for horses, so much so that Willie jokes that he'll come back as a racehorse in his next life. When Willie dies unexpectedly, Ramsey is heartbroken -- until she comes across a horse that, somehow, might be her uncle. However, her greedy aunt (Dame May Whitty) and cousins would like nothing more than to deem her insane to take over her inheritance. Now Ramsey and a professor (Glenn Ford) must prove her sanity.