Her name is Jenna Louise Coleman. She kinda looks like Selena Gomez, according to most of the internet's snap judgment. This is, of course, setting off a minor grumblestorm amidst the Doctor Who fandom. However, ANYTHING getting changed sets off a minor grumblestorm. I remember when Matt Smith was cast and everyone was like "He looks like an alien baby with encephalitis! Oh my God bring back Tennant!" Now, of course, many people consider Smith to be one of the best to ever step inside the TARDIS.
This is what will lead to Coleman's joining the cast. Either Rory or Amy (or both) will apparently meet their fate at the hands of the Weeping Angels, who will make one final appearance (until whoever picks up the mantle after Moffat has them return, probably in an episode crammed full of Daleks, too) claim some lives, and send the Doctor hurtling into a self-hating depression that he will be yanked out of by this girl.
Back again to "She looks like Selena Gomez!" And? So she looks like a pop star. Series resurrector Russell T. Davies cast two actual pop stars to be companions (Billie Piper/Kylie Minogue) before following them up with Freema Agyeman. And then Series 5 showrunner Stephen Moffat cast a model.
In fact, the practice of hiring someone young and pretty to go cavorting around the galaxy with the goofy man flying a police box through time and space has about three decades worth of precedent. It's weird as hell, but it's definitely not new. And so, I believe I'll wait to see if Coleman can actually ACT first, before I begin throwing my own grumbles into the void of the internet. I know she can talk fast, at least. Quoth the Moffat:
“It’s not often the Doctor meets someone who can talk even faster than he does, but it’s about to happen. Jenna is going to lead him his merriest dance yet. And that’s all you’re getting for now. Who she’s playing, how the Doctor meets her, and even where he finds her, are all part of one of the biggest mysteries the Time Lord ever encounters. Even by the Doctor’s standards, this isn’t your usual boy meets girl.”
I mean, personally, I would have preferred this:
But then again, that's what fan-fic is for.