A 28-year-old woman with major depressive disorder is evaluated in the emergency department after her partner found her with an empty bottle of her antidepressant (sertraline 100 mg, 30 tablets) and a handwritten note stating "I can't do this anymore. I'm sorry." She reports she took the pills 2 hours ago. Vital signs: BP 110/70, HR 88, RR 16, temperature 37.2°C. She is alert and oriented, tearful, and expresses remorse. She denies ongoing suicidal intent and says "I made a mistake." Her partner reports she has been under stress from job loss and relationship conflict over the past month. She has no prior psychiatric hospitalizations or suicide attempts. What is the most appropriate next step in her management?