When Twilight's portals release Tirek into the human world and the humans get turned into ponies, they have to unite with their ponyselves to defeat him and save both world's.
Meadow Flower attempts to cheer up Spike after she and Cloudchaser witness Rarity reject him. Things pretty much snowball from there when Meadow Flower finds herself interested in the dragon.
When shes sent to help set up a town hosting the Summer Sun Celebration with another student of Celestia's, Twilight is forced to tolerate Sunset's jokes and more in order to save Equestria.