Soro Schenirer got endorsement & blessings from the Godol HaDor, RSRH to launch Beis Yaakov movement, so this is no Heter; This is an ideal; As I have heard from a later Godol haDor on numerous occasions, because of the Beis Yaakov movement, girls are looking for guys sitting in learning to be their partners.
So what better destination, than Beis Yaakov for our gals.