This bunny popped into my head after watching Rainbow Rocks, and my art muses grabbed it and ran off with it.
I really liked the idea of Sunset Shimmer viewing Twilight as a Celestia-like mentor. Plus, it also gave me an excuse to come up with my own idea about what Twilight might look like when she reaches Celestia-tier power. Yeah, it could probably never happen in canon, but it sure looks pretty.
Twilight's hair was inspired by her namesake: the twilight right before the night, when the sky changes color and the stars start to come out. For her regalia, I gave her her Season 4 tiara and the hoof guards she wore to her coronation in MMC. Her collar was a rework of her first tiara, because it was just too pretty a design to throw away. You can't see it at the angle it's at, but it's hooked around her neck via a golden chain.