A 38-year-old woman with treatment-resistant major depressive disorder is currently stabilized on venlafaxine 225 mg daily. She presents requesting additional treatment due to persistent residual symptoms including low energy, anhedonia, and poor concentration. Her primary care provider recently started sumatriptan for newly diagnosed migraines. The PMHNP reviews her medication list and notes the potential for serotonin syndrome. When developing the pharmacologic plan to address her residual depressive symptoms while minimizing serotonin syndrome risk, which approach is most appropriate?