Final answer:
The nurse should respond by advising Wrenda to use the heating pad for no more than 15-20 minutes at a time.
Step-by-step explanation:
The nurse should respond by saying:"Apply the heating pad for no more than 15-20 minutes at a time."
This is because prolonged use of a heating pad can cause burns or exacerbate inflammation. The nurse should also recommend using other methods like rest, ice, compression, and elevation to manage the sprained ankle.