A 51-year-old female with recurrent major depressive disorder achieved full remission on escitalopram 20 mg daily three years ago after her third depressive episode. She has been in sustained remission with PHQ-9 scores consistently between 2 and 4 at quarterly visits. Over the past eight weeks, she has experienced gradually worsening low mood, anhedonia, fatigue, and difficulty concentrating, with her PHQ-9 rising to 14. She reports no identifiable stressors, no changes in medical health, and no new medications. Her thyroid studies are normal, and she denies substance use. She takes no other medications that interact with CYP2C19 or CYP3A4. She has been fully adherent to escitalopram as confirmed by pharmacy records and expresses frustration that her medication has stopped working. Her previous two depressive episodes each responded initially to different SSRIs before losing efficacy after two to three years, requiring medication switches. The PMHNP is evaluating whether this presentation represents antidepressant tachyphylaxis. Which of the following best represents the appropriate evaluation?