SJS is right, Frum women dress to impress other women! Young frum women dress to impress other young frum women. Girls dress to impress older frum women who are looking for shiduchim for their sons!
One of the things that I believe would be helpful and I mentioned it before but no one picked up on it, is if the yeshivas would give mandator sewing classes and make them fun and creative for the girls. Teach them how to take any skirt that “no longer fits” and make it longer. Or open the seams and make it a little looser. Fix a dress that is tight and make it a little looser and add something pretty and creative to the end of the sleeve to make it a little longer.
If the girls learn how to do this in school for their own Shabbos clothes or everyday clothes to make them last longer, then when they get out into the real world or when they go shopping on their own, it will be a no brainer that if the designer skirt is a little too tight or a little too short, they can add their own touch without much effort and “make it work”.
However, this will only work if it is done in the right way. If the “tznius morah” teaches the class with her whip in hand it is pointless.
In addition, if they learn to sew their own clothes they might find they have no need to go out and buy designer clothes but they can be their own designer, and who knows what the frum clothing industry would look like in the future.