Sunset has anger issues and everypony around her is well aware of her wrath. And she isnt afraid of dealing it out to those she deems deserves it, especially bullies.
Shortly after the Nightmare Moon incident, Celestia tries to help her sister get adapted to modern Equestria while Twilight and friends continue to work to know one another.
After losing her family in a fire, Sunset wanders the streets of Canterlot, doing what she has to do to survive. She finds a fellow filly on the street and the two work survive together.
When visiting an orphanage in Canterlot with friends, Moondancer realizes she actually cares about one of the fillies and hits the books to investigate.