.....Y'know, the girl clearly has problems focusing. So it makes sense that a staff- which this chapter establishes helps with focusing your magic- has such a multiplicative effect. She's like a neurodivergent kid who's actually really smart/talented, but needs extra help or nonstandard learning methods to grasp the material.
As for the panties, Imma guess they're held up by string and the author just doesn't wanna draw the threads.