Just for kicks I did copy the image, put it into Photoshop express, and used the flip horizontal feature. If you do that, the B appears on her left cheek, it's not backwards, and the picture still looks natural. But at least one of the news reports specifically says it was her right cheek, so it's not just a matter of the image being accidentally flipped (which I've seen from some digital cameras/photo software).
A couple of other things to think about: if the attacker was right handed (statistically likely since there are more righties than lefties), I think you'd more likely see the wound on the left cheek. If it were self-inflicted and the woman is right handed, you'd expect to see it on her right cheek. And I've spent too much time thinking about this.