The power was given to Cleopatra and her brother Ptolemy the 13 because her father Ptolemy died in 51 B.C. Egypt didn't pass over female children, but they did later, and Cleopatra was thought as a pharaoh. It was the family's custom to marry brother and sister, so Ptolemy and Cleopatra just did that. Ptolemy was only 12 and Cleopatra was 17. O