Personally, I think the fate changing spell was INCOMPLETE, that's why things went down hill so blindly fast. It's said in story as much. Rarity wasn't given the special talent that was supposed to come WITH the cutie mark. Basically, the spell was a buggy failure.

I've asked myself personally, what of a verse were those cutie marks WERE their natural ones, but then Twilight's spell gave them the ones they had in canon and THOSE are the ones that back fire?

Awwww, Rarity. It's nice to see another take on her muddled perspective from this episode. I wonder where she plans to go!

Sweetie belle: ... how muc did rarity drink last night.