Jahanara Begum (1614-1681) was indeed Shah Jahan's daughter AND Aurangzeb's sister - they shared the same father. She was the eldest daughter of Shah Jahan and Mumtaz Mahal, making her Aurangzeb's full sister (same parents). Jahanara played a crucial role as mediator between Shah Jahan and Aurangzeb during the war of succession and later managed the imperial household.