Actually it says "appears" not to be a high powered rifle. But, since they haven't recovered the bullet yet, or hadn't when the article was written, there' a lot of speculation and very little usefull evidence behind that statement. It might have been a bad shot, maybe a sudden gust of wind or something, that just grazed her side, with the entrance and exit wounds not all that far apart, leaving little distance for the bullet to yaw or deform, in fact the natural yaw, could have taken the bullet away from her spine and towards the outside, producing a through and through wound, with fairly small exit and entrance size.