Final answer:
Isabel possesses expert power because of her specialized knowledge of the tax program, which is valued and relied upon by her colleague James.
Step-by-step explanation:
Isabel has expert power in this relationship. Expert power is derived from possessing knowledge or expertise in a particular area that others rely on, especially if this expertise is not widespread. In the scenario described, Isabel understands the capabilities of the tax program better than anyone else, which is why James often seeks her help.
This suggests that James values Isabel's insights and expertise, indicating that her power in this relationship comes from her specialized knowledge and abilities.