0:08:59 What!? Really Celestia, that makes NO SENSE. First of all, you just said you, the all knowing princess, knows nothing of this place. Sunset has been living there for a decade, and for all you know, she has the Element of Harmony with her. You have no idea what is awaiting Twilight on the other side, and you're sending her alone!? Also, why didn't you send someone, ANYONE, after Sunset into the mirror to try to convince her to come back all this years? Or the day she went inside the first time.
Really Celestia, for the ruler that is supposed to care over all her subjects, you show a total lack of caring for your "most prized students" be it Twilight or Sunset.