To add to what others have said:

I think it's no coincidence that where she stands in relation to link would be where the master sword would be if it strapped to his back (in particular her head).

Also note worthy is that he's sword hand is open as if to show that he is about to have the sword (girl transformed) placed into his hand or she's just transformed into a humanoid figure from the sword.

Yeah and she has the blue guard just like the Master Sword too. Man im hyping myself. Best Zelda game is coming. I called it.

looks like a witch or something.

I was wondering if Nintendo could pull anything fresh and innovating with their old series. Looks like they are trying their best to pull it off.

I think she is the spirit of the Master Sword.

Dude, it's totally obvious, she's Link's Bankai!

The Master sword finally told Link her name. Although that would mean that Link would have to talk...

Nintendo can always innovate! This game is going to be great, i can feel it lol

The girl as stated by many is the master sword

Judgin from the picture, the it looks like its going to be part of the childhood timeline of the series or at least windwaker since the fairy looks really similar to the ones from WW. Anyway it going to rock.

I heard she is the Master Sword.

this, its so obvious now.