I'd also like to point out if she does this by superheating air the effect will be more like lightning than a bomb.

And her explosions wouldn't be focused enough to blow a leg off by that means, it would blow the rest of the body away as well.

....
I'm such a fucking nerd omg.
http://i3.kym-cdn.com/photos/images/original/000/517/111/fbd.jpg