I guess now she's... *puts on sunglasses* ..the Twilight Princess. YEEEAAAAAAAAAHHH!!!
No but in all seriousness, I don't see why everyone is worked up about this. MLP: FiM's INTENDED audience (regardless of who actually watches it) is little girls. Little girls like princesses. It makes perfect sense for them to make a pony princess, as it might attract more little girls to watch the show. So, really, you can get mad, but you have to remember who the show is aimed at.
Also you never know, it might work.. maybe..