The reason for the halacha is that hair is erva. Period. [At least that’s the way I was taught] Otherwise, single women would not be allowed to wear hats ever as its a sign of being married. Or a woman could just wear a large sandwichboard sign that says “I’m married” (and sell advertising on it to make more money).
Or a ring.
Sefer Ba’akavot Rochel (AKA daughters of dignity), as I have said before, (and as the cover states) is more of a “Hashkafa” sefer than a “Halacha” sefer.
Not as if there is anything wrong with Hashkafa, C”V.
SJS: Tznius for women as defined in this day and age stems from multiple reasons. You are discussing the “Brachos by men” aspect.
I think ASF is discussing the “hirhurrim by men” aspect (correct me if I am wrong).