Can the Muslim woman expose her hair to a non-muslim woman such as in the hair saloon ( in the presence of only women )? Thank you.

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.

The Awrah (those parts of the body which must be covered) for Muslim woman in front of another Muslim woman is between the navel and the knee. But the Awrah for the Muslim woman in the presence of Non-Muslim woman is the whole body except what appears at the time of work, like face and hands. 

Allah knows best.