When in Ihram, women have to keep from cloth away from their faces, as in Ihram, the Ihram of women is in their faces. If there is any fear from non-Mahram people, then she might cover her face in such a manner that cloth does not touch her face. Thus, there is a Hadith in Sunan Abu Dawood:
Translation of Hadith: The mother of the believers, Hadhrat Ayesha (May Allah be well pleased with her) said: Riders would pass by us, when we were with the Holy Prophet (Sallallahu alaihi wa sallam) in Ihram. When the riders would pass by us, every one of us would put our Dupatta on our faces and when they would move forward, we would remove it.