A 6-month-old girl from Bangalore is brought to the emergency department with severe hypoglycaemia (blood glucose 28 mg/dL), hepatomegaly, and lactic acidosis (pH 7.18, lactate 12 mmol/L). Liver function tests show markedly elevated transaminases and hyperuricaemia (uric acid 9.2 mg/dL). Enzyme assay confirms glucose-6-phosphatase deficiency. After immediate IV dextrose and stabilization, what is the most appropriate next step in long-term management?