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 is His slave and Messenger.
It is not permissible for your wife to travel without a Mahram (i.e. the husband or any person whom one is permanently prohibited from marrying due to suckling, marital, or blood relations) even if her employer demands her to do so.
For more benefit on the ruling of a woman travelling without a Mahram, please refer to Fatwa 83912, and to Fatwa 82399 on the pre-conditions for a woman to work.