“If virtually all frum girls are torah-educated and versed in chumash, Rashi, Rambam, and other varied Jewish subject matter, including halachos, why aren’t they all dressing within normative tznius guidelines – even within the spirit of halachah?”
Perhaps this is the problem. Instead of making sure girls are up all night studying for tests that ensure their fluency in Rambam and other subject matter and instead schools taught hilchos tznius and basic hashkafa, girls would know what is and what is not considered proper according to halacha and will also know how to behave within the spirit of the halacha.
More girls today know more Rambans than many of the Rambans own talmidim and many bachurim know more R’ Chaims than most of the gedolim who lived in Brisk yet we are in a situation where we are discussing the fact that females dont dress according to halacha and men are doing little to nothing to stop it.