A 32-year-old woman who is four weeks postpartum and exclusively breastfeeding presents with worsening major depressive disorder. She has a pre-pregnancy history of recurrent MDD with two prior depressive episodes, both successfully treated with sertraline 150 mg daily. She discontinued sertraline in the first trimester against medical advice due to concerns about fetal exposure. Her current PHQ-9 is 20 and EPDS is 18. She denies suicidal ideation and psychotic symptoms. She is strongly motivated to continue breastfeeding and is anxious about any medication entering her breast milk. The PMHNP is developing a treatment plan that addresses both her depression and breastfeeding goals. Which approach is most appropriate?