Final answer:
Psychotherapy, specifically systematic desensitization, is the most likely approach to reduce the client's anxiety level.
Step-by-step explanation:
The woman in this scenario is experiencing symptoms of anxiety while riding in elevators, and a physician has found no physiological basis for these symptoms. The most likely approach to reduce the client's anxiety level is psychotherapy. Among the options given, systematic desensitization is a psychotherapy technique that could be used to help the woman overcome her fear of elevators.