A 18-month-old girl from a low-income family in Delhi presents with a 3-month history of poor feeding and abdominal distension. On examination, she weighs 8.5 kg (expected 11–12 kg), has bilateral pitting edema of the legs and face, and mild hepatomegaly. Her hair is sparse, thin, and shows a characteristic alternating pattern of pigmented and depigmented bands ("flag sign"). Serum albumin is 1.9 g/dL, and prealbumin is 12 mg/dL (normal 20–40). Which complication is she at highest risk for during the initial phase of nutritional rehabilitation?