A 5-day-old female neonate born at term to a G2P1 mother (first child had jaundice requiring phototherapy) presents with visible jaundice. The infant was born vaginally after an uncomplicated pregnancy. Maternal blood group is A Rh-negative; infant is A Rh-positive. Serum bilirubin is 16 mg/dL (total), with direct bilirubin 0.5 mg/dL. Hemoglobin is 13.8 g/dL, reticulocyte count 4.2%, and blood smear shows microspherocytes. Direct antiglobulin test (DAT) is strongly positive (3+). What is the most likely diagnosis and the most appropriate immediate management?