The Gemara in Sotah yud beit: daf alef tells us that when Miriam HaNeviah was rejuvenated she became so beautiful that men would become aroused by her and rush home to their wives for the *ahem* obvious reason.
Now was Miriam HaNeviah not Tznius? Was she responsible for bitul zerah or aroyos? Surely we can assume she wasn’t dressed immodestly but she was nevertheless arousing men. The whole Tznius argument rests on women arousing men. The effect was therefore the same. Yet we don’t seem to view Miriam that way. Nor do we blame her for her effect on men.
Now I’m sure that there’s a dozen ways to wiggle out of this but the point is simply that Miriam was not held responsible for the reactions to her beauty. She wasn’t told to cover up her face because it was having an effect on men or hide out in her tent. Miriam was beautiful and that was something to be appreciated. She was not held responsible for how men saw her or how they reacted to her. She was a Tzanua through her own behavior. Why can’t we use that as a model?