My Little Pony: The Runaway Rainbow(2006)

Overview:

Rainbow Dash loves the time of year when Ponyville and Breezie Blossom are all about celebrating rainbows. Meanwhile in a new magical place called Unicornia, Rarity is being taught how to be a Unicorn Princess and the importance of making the first rainbow of the season. But she is quite a little rascal and embarks on an incredible ride, a huge adventure (with lots of mishaps) as she tries to get back to Unicornia. Rarity soon realizes that getting home in time to create the first rainbow of season is not an easy thing to do --- but it is fun!