Mary, who has a great fear of flying, has been instructed by her behavior therapist to take a brief ride in an actual airplane. if mary follows her therapist's instructions, then she'll be engaged in

in vivo exposure therapy

Explanation:

This kind of therapy is based on the idea that the patient should face the trigger that produces discomfort. Although  it can be thought as a counterproductive kind of therapy, it is necessary to take into account that the professional should be very well prepared in order to recognized the level of anxiety the patient is going through when the in vivo exposure therapy is taking place, and it is possible to simply stop it when they consider it is not healthy for the patient.

On the other hand, the therapy is very well known to help patients facing diferent kinds of phobias and to be very successful.