Tzanuah means absent?
Women are not absent from the Pesach story or from Tanach or Talmud. But today its tottaly normal to call discrimination against women Tznius. Tznius has tottaly lost its meaning.
I don’t know why there are no daughters in the Hagadah, but its definitely not related to tznius. Women should be able to talk and ask questions in their own home, from their own father. And the Torah has plenty of instances of this.