I was going to write a story about Starshine but never got around to it.
 
Starshine is a loner, kind of young, who never learned how to control her powers and it gets her into trouble a lot. When she accidentally steals Rainbow Dash’s weather manipulating ability bad stuff starts to happen (this middle part - most of the story - is what I never worked on). Twilight manages to find a solution and the balance is restored. Twi gives her one of her classic lectures, and I don’t know, maybe takes her in as a student or something. I didn’t figure out that part either.
 
This picture is from that lecture scene, where Starshine must own up to her mistake.