A 32-year-old woman presents to the primary care clinic with a 6-week history of tearfulness, difficulty concentrating, sleep disturbance, and appetite changes. These symptoms began shortly after she finalized her divorce, which she describes as "heartbreaking" and stressful. She reports feeling overwhelmed, tearful at work, and easily fatigued, but denies any suicidal ideation, flashbacks, nightmares, or history of trauma. She has no prior psychiatric history. On mental status exam, she appears anxious, tearful, and her mood is depressed. She continues to work full time but notes decreased productivity and difficulty sleeping. Which of the following is the most likely diagnosis?