Final answer:
A wife making healthcare decisions for her incapacitated husband is acting as a health care proxy, which is established through a legal document allowing her to make medical decisions on his behalf.
Step-by-step explanation:
A wife who is legally authorized to make healthcare decisions and act on behalf of her incapacitated husband is acting in the capacity of a health care proxy. This role is typically designated in a legal document that specifically appoints a person to make medical decisions for the patient when they are unable to express their wishes themselves. These decisions can cover a wide range of medical interventions and treatments, and the appointment of the proxy is intended to ensure that the patient's healthcare preferences are respected, often in alignment with their living will or advance directive.