Is it permissible for a woman to travel for Hajj without a mahram if she is a doctor and the campaign obliges her to travel with them due to the unavailability of a substitute at the present time?

It is not permissible for a woman to travel for the obligatory Hajj or the obligatory Umrah without a mahram, due to the Prophet's (peace be upon him) saying: "A woman must not travel except with a mahram." The fact that the campaign requires a female doctor to travel with it, and there is no time to search for another doctor, does not make it permissible for you to travel with them without a mahram.