Allie Nadeau, aged 11, was riding horseback when she was struck by a bullet in her butt. Wsmv reports that authorities believe that the bullet, which hasn't been recovered, was fired by a "high powered rifle".
The video clip show what could be a .303 or 30-06, so that high-powered part sounds about right. Maybe a hunter shot and missed? The bullet was left inside the poor girls buttock because removing it would cause more damage, so I don't suppose it got lodged against her pelvis.
But it did penetrate a thin metal sheet that constitutes the wall of the stable she was in. with enough disctance between the shooter and the stable, this seems plausibe.
If anything, this should teach us that you better be sure of your target, and what is behind it!