In the human world, Principal Cinch gets desperate after losing Twilight to Canterlot High. So she convinces Starlight Glimmer to attend Crystal Prep. Though due to her past with Sunburst, she isn't as favorable to Friendship as Twilight was. The students of Crystal Prep, getting use to accepting friendship under Twilight's example, try accepting Starlight as one of them. But with Starlight's bitterness towards superiority, Crystal Prep's reputation makes it even more difficult. And with Starlight's cleverness, she assures Cinch doesn't cause any trouble for her or anyone else. She stumbles upon Twilight's private research room and discover the designs for her Magic spectrometer. With some of Starlight's improvements, she succeeds in easily accessing Equestrian Magic.
This should be a spin-off EQG film or a fan fiction.