you really have an unfounded negative opinion about jewish women which borders on loshon hora
Mammele, if you want to accuse someone of loshon hora, please understand the implications of your accusation being incorrect (even if well intentioned). This discussion has been (IY”H) l’shem shamayim, but accusations like that tend to kill the productivity of a torah discussion. My very well-founded opinion, as you’ll see below, if anything is a shevach about jewish women. Also, note Curiosity’s response to your case (not to mention that it was also a woman who gave you tochachah).
There is every chance she will heed the Torah once advised that she is acting improperly.
Although the statement itself is true, this is where your logic fails. To see this, note that a)her husband and rav know that she covers her hair this way (dan l’chaf zchus – you must assume this for a stranger) and b)she is following her husband or rav’s opinion, even if it is wrong (again, you must assume she is following an opinion because of dan l’chaf zchus combined with the knowledge that there are rabanim, even if wrong, who say that covering the hair less than fully is fine). There are entire communities whose rav does not correct them on this (again, I’m not saying it’s right or wrong, I’m saying that they rely on their rav).
So therefore, when a stranger approaches this jewish woman and gives her tochachah, she will not accept it because a)her husband and rav haven’t corrected her and b)she is following a psak (not necessarily yours, but a psak nonetheless). She will rightfully get defensive because who is some stranger to come tell her that her husband or rav is wrong? Therefore, you see, it is not proper for a stranger to give tochachah in this case.
And Mammele, now you see that this is a shevach of jewish women for assuming that they listen to their rabanim on matters of halacha.