This thread could go on forever but the bottom line is Tznius has to start at home. Your schools and Rebbetzins dont buy your clothing. Its the mothers who shop for the girls and women who shop for themselves. The mothers have to make it clear that untzniusdig clothing is not allowed in this house. Be firm about it and make it clear that theres no room for compromise. If a parent pays for clothing for their daughter that isnt tznius then they are accessories to the averah. A teenage girl usually cant afford her own clothing so the parents have to say “you dont buy tznius clothing I dont pay for your clothing” it may sound harsh but hey it will work.
Another point is a husband has to set up a Torahdig house where the wife wouldnt consider bringing home such clothing for herself. It has to be something discussed and clarified that it wont go on in your family. You cant say “oh its just one outfit she probably didnt realize…” it will become her whole wardrobe very quickly.
I agree with what some other people mentioned regarding learning/reading books on tznius. Considering how big of a nesayon it is for girls and as I guy I will really never know, all I can say is that the nesayon requires constant work which means constantly learning and relearning the Halachos and all the inyanim of tznius. I know that if I find myself having a hard time in any area I focus on it and spend extra time learning those halachos and hashkafos. Same should be any man or women who finds themselves having a hard time combating their yetzer hora.