Final answer:
The nurse demonstrates letting go by spending the afternoon with friends, which allows for mental relaxation and a refreshed perspective upon returning to the problem.
Step-by-step explanation:
The action that demonstrates letting go in a problem-solving context by the nurse is C. Spending the afternoon with friends. This step indicates a deliberate break from actively thinking about the problem. It involves engaging in different activities that allow for mental relaxation and distancing from the immediate issue. This break can be beneficial for cognitive processes as it provides time for subconscious thinking, which can lead to a refreshed perspective upon returning to the problem.