Is it permissible for a woman to use the car's front mirror to clean her face in front of road users?

If the driver is a foreign man, it is not permissible for a woman to unveil her face or clean it in front of him, because it is considered part of the awrah that must be covered. Also, it is not permissible to be alone with him (khalwa). If the driver is a woman or a mahram, and she is safe from being seen by men, then there is no objection to that.