While watching the movie, have 你 noticed that Rain's feather stayed on the whole time, even when she and spirit were swimming? Astonishing! Lets see what 你 thought in your answers.
At first I thought it was braided in, but then at the end Little Creek just slipped it out really easily. I think it might have been a mistake on the animator's part.
Usually native americans have strings/clips to keep the feather in the hair, 或者 they just braid it in. It probably WAS a mistake... good eye, I never noticed that.
I think that the Indians put it in so that it marked her as an Indian horse, and also, maybe he didn't just slip it out, maybe it was braided but he knew how to take it out easy.