Is it permissible to continue in a mixed-gender work environment where the woman—who is fully committed to the legitimate Islamic hijab—is in a place isolated from men and only interacts with them out of necessity and within the scope of work, especially if the work helps her overcome severe obsessive-compulsive disorder?

The work mentioned is not forbidden (haram), and there is no blame upon you for continuing in this job. It is recommended not to surrender to satanic whisperings (waswas), to avoid sitting alone, and to frequently supplicate to Allah. It is also recommended to frequently remember Allah (dhikr) and recite the Qur'an, and to have righteous companions with whom you can study knowledge, memorize the Qur'an, and cooperate in goodness.