Final answer:
The nurse should advise the client to use the nasal spray only when absolutely necessary to avoid dependence and rebound congestion.
Step-by-step explanation:
When a client has been using a decongestant nasal spray for three months, it is important to provide the appropriate response as a nurse. In this case, the nurse should advise the client to use the nasal spray only when absolutely necessary. Prolonged use of decongestant nasal sprays can lead to a condition known as rhinitis medicamentosa, where the nasal passages become dependent on the spray and rebound congestion occurs when the spray is stopped abruptly. Therefore, it is best to use these sprays sparingly and for a short duration to avoid dependence and rebound congestion.