I think it is particularly complicated in Europe ...http://www.huffingtonpost.com/william-fisher/europes-great-cover-up_b_583364.html
The conditions in N America or Israel, would be completely different for Jewish women's dress.
Hypothesis ... this is an Orthodox Jewish school
If the school allows students from outside the Orthodox community, then they can't enforce standards on the parents, but they can on the children, as a condition of admission.
If the school only allows students from within the Orthodox community, then the parents and children are both subject to the dress code all the time
In Europe however, there is a state driven "laicity" particularly in France. This article is about Belgium, which is half French. Don't know how far Belgium goes with "laicity". Laicity would enforce a secular dress code on everyone. We don't have anything like this in N America, outside of Orthodox Jewish communities or Amish. Israel is even more secular than Europe or N America ... except in very small Orthodox enclaves.