Strenuous exercise has caused her body to be in oxygen debt, and she is breathing hard while lactate is transported to the liver. This is a result of anaerobic respiration.
During exercise, the muscles use the oxygen present there and become deprived of oxygen. Due to less oxygen, the anaerobic respiration occur in the muscles, to overcome this, the heavy breathing takes place. heavy breathing brings the oxygen to the muscles.
During anaerobic respiration, the glucose is broken down into the lactate and the lactate is transferred to the liver for the gluconeogenesis and to maintain the constant supply of the glucose to the muscles.