I thought it be interesting to portray how Sunset initially fell from grace through her eyes. From her point of view, this was probably what it seemed like. She was chosen to be Celestia’s student. She tried to prove her worth by working really hard and learning as much as she could, but ending up trying to learn too much too fast and before she was ready for it, and took Celestia not teaching her everything she wanted to know as a sign that she didn’t think she was worthy and trying to hold her back. Then after she had been trapped in the human world, she discovers that Celestia went and gave everything Sunset had been working for to Twilight. I can kind of understand why Sunset felt like Celestia went back on what she promised to give her and instead gave it to Twilight, so I can see why she would try and take it by force. Yeah, I know there’s more to the story than that, but I’m saying, this is likely Sunset’s perspective on how things went down.