Police in southern Hyderabad city told BBC Hindi they want to know if Aradhana Samdariya was forced to fast.
Her parents have insisted she voluntarily fasted as prescribed in Jainism, one of the world's most ancient religions.
The case has sparked a debate about the practice of religious fasting in India.
Reports said Aradhana lived for 68 days on boiled water. Two days after she called off her fast last week, she was dead.