Harry Potter and Lady Malfoy

What if there was a curse placed on the Malfoy family to only have one male heir per generation, and it was broken with the birth of Draco's older sister. However, she was born during the war and kept hidden since she would have control of the ministry with the sacred 20 families. She was adopted by Sirius Black and Lily Potter and turned 4 months before the 'defeat' of Voldemort.