The photo was a fake and Emma never posed nude or topless. The photo is done well enough that it actually looks legitimate, which may be the source of confusion. Emma announced that she was pissed and there would be possible legal repercussions for the nude photo.
Emma states this as her reason for leaving brown:
As you know, I love Brown and I love studying pretty much more than anything but recently I’ve had so much to juggle that being a student AND fulfilling my other commitments has become a little impossible
More about it: