Final answer:
The nurse should prioritize instructing the client to report any muscle tenderness to their healthcare provider.
Step-by-step explanation:
The nurse should give the client with high cholesterol the priority instruction to report any muscle tenderness to their health care provider. This is because muscle tenderness can be a sign of a potentially serious side effect of simvastatin called rhabdomyolysis, which is characterized by the breakdown of muscle tissue. Rhabdomyolysis can lead to kidney damage and other complications.