Through the Mirror — G.M. Berrow

Welcome to a Whole New World...

When her new crown is stolen from the Crystal Empire, Princess Twilight Sparkle pursues the thief, Sunset Shimmer, into an alternate world, where she finds herself turned into...a girl!

To regain her crown and return to Equestria, Twilight must learn to fit in this strange new world and defeat Sunset Shummer in a competition to be crowned princess of the Fall Formal at Canterlot High. Luckily, she has the assistance of Spike and five girls who remind her of a certain group of friends back home...