Pretty sure shiftmaster was referring to sil instead of Sonia/Minnie, as that's who penny's fighting. 

But the real reason why Sonia is so powerful is because the strongest thing any woman can be in anime is a maid. Penny would fair much better against everyone if she looked like this:

[img]https://78.media.tumblr.com/7a24d99fba5039f457af6365d0ac5b25/tumblr_ozdtnomCg91w6599so1_1280.png[/img]