To save what remains of the Griffon Kingdom, Celestia is going to have to give them a new leader. Unfortunately for Gilda, she's the only one available for the job.
Twilight Sparkle, a pony turned dragon, might be Princess Celestia's personal student, but that doesn't exclude her from the trials and tribulations that come with growing up.
The Flim Flam brothers made a number of claims about the Miracle Curative Tonic, and even though one was brushed aside there is still one pony in Ponyville who's interested in adding a few years.