Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.
There is agreement among Fuqahaa that a woman has to cover her face in case of fearing temptation, but they differ concerning this issue in case of not fearing temptation.
We believe that the correct opinion is to cover the face in both cases. This is the opinion of al-Hanabila and the most correct opinion of al-Shafi'iyah. It is supported by Qur'an and Sunnah.
So, we tell our sister that you are to cover your face wherever you are as long as there are alien men, i.e. in their presence, whether it is possible to be harmed and disturbed or not.
Any other saying in this concern is not correct, and the situation of women in the Prophetic era give us the best example. They used to wear Hijab and cover their faces without considering harm or disturbance.
Allah knows best.