Its important to note that she was the last of a dynasty that reigned Egypt since 334BC. Established by the Greek Macedonian General that was left by Alexander the Great after his conquest of Egypt and it territories. This was a Greek dynasty and therefore a Greek royal family that would have over the years made political marriages with the other kings of the region... in particular the Jewish Dynasty of David.... making the possibility of this Woman and her Children descendants of David.
also see http://bmcr.brynmawr.edu/2008/2008-09-11.htm also see http://www.houseofptolemy.org/housecle.htm
from... http://interoz.com/egypt/cleopatr.htm
http://www.nationalgeographic.com/events/cleopatra/cleopatra-the-legend/