A woman's son-in-law is a Mahram

A: A woman's son-in-law is a Mahram (unmarriageable relative), so it is permissible for him to see what he is permitted to see of his mother, sister, daughter, and all other Mahrams. Therefore, if the woman covers her face, hair, forearms, and so on in front of her daughter’s husband, this is a kind of exceeding proper limits in the ruling of Hijab. Refusing to shake hands with him when meeting is also a kind of extremism. This may lead to problems or a breakdown in relations. Accordingly, she should avoid being extreme in this way unless she has some reason to doubt him or she feels that the way he looks at her is not proper, (Part No. 17; Page No. 357) in which case she is doing the right thing. May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.