Dark side? Meeehh....
I don't see a point when her persona as a whole doesn't have anything to do with darkness. Applejack's lying, Pinkies Depression, Rarity's greed, those all have multiple ways of being looked at and even used for plot elements.
Mean Fluttershy is just... well. Mean. There isn't much there to dissect.
On the other hand, FlutterBat needs to happen.