She has seen him do more amazing things, but she thinks him stepping on the guys foot during battle was an indication of a widening gap? If anything she should know he's holding back right now since he hasn't taken off his weights.
@degenerateafro I think that's the point. MC took off only 1 weight and is basically going easy on an actual superior (in rank, if nothing else) and is still pretty much playing with him. She knows he's strong for beating the Ogre, but he had to go (almost) all out and was pretty injured afterwards. Right now, all he's taken is just a scratch