Crapplejack

I was thinking about Pinkie Pie joining the apple family and Applejack and crew welcome her with a fancy song talking about what the Apple Family is all about, but you theory isn't bad either.

Chrysalis. She's a complete idiot. "This purple unicorn thinks that I'm Cadence so let's be an ass to everyone so that she'll notice that I've changed, and eventually try to stop the Wedding " "Hey this Twilight Sparkle seems to have a good relationship with the pony I took the looks of and trapped into the caves, so let's trap her too after she comes to think that I'm the true Cadence so that they're able to reunite, return here, and kick my butt " "Hey, let's show my true self, even though nobody can say that the Cadence that just appeared is the true one, so I'll take the risk of losing against Celestia " "Hey, the wielders of the Elements of Harmony are running, oh let's just say that they can run but not hide and take once again the risk of getting my ass kicked " "Hey I'm about to take over Canterlot, let's stay near the window and sing an useless reprise of the last song while the good guys are utterly free to do whatever they want to " It's always nice to see how people hate on Sunset Shimmer just because she is a human, and as such doesn't have any magical power in her world.