A 10-month-old girl born in Delhi presents with her parents with a 2-month history of poor feeding, constipation, and irritability. Physical examination reveals bleeding gums, perifollicular hemorrhages on the lower extremities, and poor wound healing from a recent vaccination site. Hemoglobin is 9.2 g/dL with microcytic indices. Serum vitamin C level is 0.2 mg/dL (normal >0.6 mg/dL). X-ray of the knee shows a characteristic 'scorbutic rosary' with a dense metaphyseal line. What is the most appropriate next step in management?