Answered by Sayyidi Habib Umar bin Hafiz (may Allah protect him and benefit us by him)
What is the ruling on a woman uncovering her face when in a state of ihram (pilgrim sanctity)?
It is permissible for her to uncover her face but it is preferable for her to cover it. The Prophet ﷺ chose for his wives and the women of his Household that they uncover their faces when not in the presence of strange men (meaning men that it would be permissible to marry). Sayyidah Aishah said: “When men on horseback approached we would lower our veils over our faces and when they went away we would lift our veils.” This is the choice he made ﷺ for his wives, the Mothers of Believers, nine of whom made Hajj with him. If a woman is on her own or with men who are unmarriageable kin (mahram) it is impermissible for her to uncover her face until she releases herself from the state of ihram (pilgrim sanctity). When she is in the presence of men whom it is permissible for her to marry it is permissible for her to cover her face. If she does cover her face the scholars differ on whether she must pay an expiation. In the Maliki school if she covers her face without that covering being attached with a cord or the like then she is not obliged to pay an expiation. The relied upon opinion in the Shafi`i school is that she must pay the expiation. She can choose between fasting three days, slaughtering a sheep or feeding six poor people.
In summary, it is permissible for her to uncover her face as is shown in the hadith when a woman who was in ihram approached the Messenger of Allah ﷺ to ask him a question. Her face was uncovered and when Fadl bin Abbas who was riding behind the Prophet on his camel looked at her, the Prophet turned his face away from her. However, the Prophet taught his wives and womenfolk to cover their faces in the presence of strange men, and this is preferable.