Is it Islamically permissible for a Muslim woman to adhere to the full Islamic dress in a Muslim country, and then revert to wearing a different (less Islamically compliant) attire upon her return to France due to work circumstances?

Women are commanded to observe hijab and cover themselves from non-mahram men. This is a general command, not restricted by place or time. The obligation to adhere to it does not fall away merely due to harassment, unless severe harm is feared for her.

It is not permissible for a Muslim to reside in lands of disbelief if they cannot openly practice their religion, nor is it permissible to work in mixed-gender environments except in specific cases. We recommend fearing Allah and acting in accordance with His law.