A quick response to Joseph –
“How does the Mesorah change just because most people changed from following their Mesorah?”
Yes it does, read my earlier post explanation. The mesorah as per Rambam and SHu”A was that girls i.e. besulos covered their hair as well.
“Dat Yehudit” as explained earlier, is all relatively-minhag-based. Modesty (not ervah Do’raisa) has always been based on what was relatively considered modest at the time n region.