Maybe the Princess of Destiny.I mean, so far she´s managed to change cutie marks with her magic, which, I may add, are directly linked to their destiny, and she managed to alter the course of time during her little time travel.Both feats imply that she is very skilled at using magic that changes one´s destiny, so it would be very likely that she´d be the princess of Friendship.Speaking of change, maybe that´s what Sunset is good at (sorry, got too much free time): She managed to turn the Element of Magic evil and use it for herself, and she turned SciTwi good a few movies later.So yeah, we´ve got Twilight, who´s good with magic in general, Starlight, who´s good with destiny-related magic, and Sunset, who´s good with change-based magic.I´ve got this little theory that there is always one or two ponies whose special talents give them a wider variety of abbilities than the average pony, and I think I just gave enough evidence of this actually being the case.