If the mother wishes her children to be educated by the ultra Orthodox, then obviously there is a dress code that should and must be conducted at all times outside the home. I don't understand why the mother would'nt want to comply. If this is an issue for her, then she can always choose a more liberal school for her daughter.
Saudi FM: We hope Iran uses sanction relief for development, not nefarious activities (Reuters)
from the article: Ultra-Orthodox school bars girl over her 'mother's immodesty'