A 32-year-old woman from rural Maharashtra presents to the emergency department with severe hypoglycemia (blood glucose 35 mg/dL) and altered mental status. She reports a 3-day history of vomiting and inability to eat following acute gastroenteritis. On examination, she is diaphoretic and confused. Serum lactate is 1.2 mmol/L (normal), serum alanine is low, and liver function tests are normal. Which enzyme deficiency would most directly impair her ability to maintain blood glucose during this fasting state?