Is it permissible for a woman in a state of ihram to wear the niqab, and does her wearing it entail the non-acceptance of her Hajj?

It is not permissible for a woman to wear the niqab (face veil) during ihram, according to the Prophet's (peace and blessings be upon him) saying: "A woman in ihram should not veil her face nor wear gloves." However, if a woman wore the niqab out of ignorance, there is nothing upon her, and her Hajj is valid.