Sunset never intended to hurt anyone. She simply had a dream of who she wanted to be. And nothing's more gut-wrenching than realizing real life simply doesn't include your life-long dream...
Sunset has decided to return home... wherever that may be? The orphanage where she was left? The castle where the princess had emotionally abandoned her? She walks the foreign but familiar world, hoping to find something to make her life worthwhile.
Princess Celestia finds a baby Changeling Queen during her travels. She had intended to bring her back to Canterlot only temporarily, until she could find the hive the Queen belonged to. For now though, the Changeling Queen was just Twilight Sparkle