Reining is most common in north Texas, Arizona, and the Southwest, not the Northwest states.
The cars in Pittsburgh all have front plates. Cars in Pennsylvania don't have front plates.
Flicka changes from an Arabian to a Quarter horse, with the last scene having a mare and foal. The mare is much older than Flicka proclaims to be.
After getting back from her ride into town when Carrie is leading Flika from the barn, she becomes a he and has male horse genitalia.