Princess Celestia and Luna announced their retirement and Twilight Sparkle to be their successor, and ascend the throne of Equestria. Twilight is stressed about it, but her mind is focused on her former assistant at Ponyville's School of Friendship named Cozy Glow.
She finds her punishment too harsh, therefore she wants to at least try to convince her to be a good pony and release her from Tartarus.