With that another question pops up. How did Sunset Shimmer knew of Twilight's coronation and crown? I have seen a discussion about that, so that can at least answer that, but it's just a theory. A little revenge against Celestia for expelling her from the castle?(I've seen a picture from the comics that some royal guards were escorting her somewhere, but I don't know exactly why) And she did say that the school wasn't her objective, it was conquering Equestria with her "army" and power from the crown, to which she could do something since Cadence say's that it's Equestria's most powerful weapon against evil. So that would leave them defenceless.