Will transferring my sister to an Islamic school help her accept my mother’s modesty?

I am actually facing a big and serious issue. My mother is a complete parda nasheen lady she wears niqab, burqa, khuffain, black gloves. Not a single inch of her is visible. As a son we all admire her for her modesty. But as my sister grew she started asking her to do this type of clothing and my sister who is a bit modern in clothing and thinking misbehaves with my mother as she is a female no one beats him but I scold him very much. She use to wear jeans and tops from childhood now as she is 14 years old she is asked to wear niqab, burqa, gloves and khuffain. She was earlier studying in unity college Lucknow but now we have transferred her to Jamaitul Momina school Lucknow which is an Islamic girls school so that she stays with the other girls of her age and starts doing what my mother do. As we are very tense whether doing this whether she will get marriage proposals or not. Please answer me in details.