A 32-year-old woman is 6 weeks postpartum and exclusively breastfeeding. She presents with worsening depressive symptoms including persistent sadness, difficulty bonding with her infant, insomnia (beyond what's expected with a newborn), and intrusive thoughts about being an inadequate mother. Her Edinburgh Postnatal Depression Scale score is 16. She was previously stable on sertraline before pregnancy and asks whether she can resume it while breastfeeding.