Cleopatra was the daughter of Ptolemy VI and Cleopatra II, who were brother and sister, as their own parents had been. Her childhood was presumably not a quiet or particularly stable one, considering the tumultuous relationship her parents had with each other and their brother and co-ruler, Ptolemy VIII. Her father died in 145, when she was somewhere between the ages of 10 and 15, leaving the way for her uncle to take the throne and marry her mother.
Cleopatra married her uncle as well about three years later. She was incorporated into the dynastic cult around the same time and provided with her own priest. She, her mother, and Ptolemy VIII proceeded to rule as a triumvirate. This lasted for about 10 years until her mother decided she would rule better on her own and kicked Cleopatra and Ptolemy out of Egypt for three years.* The two of them eventually managed to depose Cleopatra II and return to their thrones in 127. The three reconciled by 124 and returned to ruling as a triumvirate.
With Ptolemy, Cleopatra had five children, two sons (both named Ptolemy) and three daughters (Cleopatra VI, Cleopatra Tryphaena, and Cleopatra Selene). On her husband’s death in 116, she and her mother continued as joint rulers with Ptolemy IX, the elder of Cleopatra’s sons until her mother’s death the following year. Around this time, Cleopatra decided** that that her younger son should rule instead of the elder and so crowned him Ptolemy X, sending Ptolemy IX away. Unfortunately for her, Ptolemy X would turn out to be perhaps the most unpopular ruler of the Ptolemaic dynasty, making the last five years of her life and rule very unstable. She died in 101 BCE, possibly (possibly not) murdered by her younger son.
*The fact that Ptolemy VIII was not particularly well-liked probably made it easier for her.
**Or acted on an earlier decision.
Shipley, Graham. The Greek World After Alexander. New York: Routledge, 2000.
Justin, Epitome of the Philippic History 38.8 - Forumromanum.org
Justin, Epitome of the Philippic History 39.4 - Forumromanum.org
Pausanias, Description of Greece 1.9.1 - Perseus
Cleopatra III - Egyptian Royal Genealogy
Cleopatra III - Livius.org
Cleopatra III Euergetes - virtualreligion.net