Non-Muslim women living in Muslim countries are not required to wear Islamic dress. If a non-Muslim woman wears a head-cover willingly to preserve her decency and chastity, this is a praiseworthy act on her part. If she does not, she is not to be enjoined to do a thing not required from her in her religion.
Sheikh Ibrahim Salih Al-Husaini, Mufti of Nigeria, states the following: It is known in general that the non-Muslim women (the Christian and Jewish ones) who live in Muslim countries are not required to behave like Muslim women with regard to the way of dress and dealing with men. If they are married to Muslim men, it is then that they are to abide by what Muslim women are to do in these regards.
Otherwise, we are not to enjoin the non-Muslim women who live under the protection of Muslim countries to adhere to what Muslim women are to stick to. We, rather, are to let them on their own. Such an attitude stems from the Islamic teachings as to religious tolerance and peaceful coexistence with non-Muslims.
Mind that Islam has not prescribed a certain color or form for women’s Islamic dress. What it ordains in that regard is that the dress be covering the whole body, non-transparent, non-shaping, and usually not beautified for seduction. Also, a Muslim woman’s dress is not to resemble men’s way of dress. Both men and women are not to dress in the same way like each other.
To sum up, non-Muslim women who live in Muslim countries are not required to dress like Muslim women, unless they want so themselves, for we should not enjoin them to adhere to a thing they are not principally required to do in their religions.