Daughter of Ptolemy VI & Cleopatra II
Niece-consort of Ptolemy VIII. 

Cleopatra was 15 when her uncle married her & made her his co-regent (140 BCE). She remained a loyal wife during her husband's running feud with her mother & accompanied him into exile (130 BCE). Her loyalty was rewarded three years later when she replaced her mother as reigning queen of Egypt.  Yet she was instrumental in the eventual reconciliation of her husband & mother (124 BCE). She became senior ruler of Egypt when her mother died (115 BCE) & played a pivotal role in the rivalry between her sons. After years of feuding with her oldest son (Ptolemy IX) she expelled him from Alexandria (107 BCE) & replaced him with his younger brother (Ptolemy X). Now at the peak of her political power she presumed to do what no other female ruler of Egypt had ever done: act as priest in the royal cult (105 BCE). Her dominance was short-lived, however, since her favorite son (Ptolemy X) soon had her murdered.

References: Josephus, Antiquities 13.80-82, 109, 116, 120.
                  Pausanias, Description of Greece 1.9.1-3.
                   Justin, Epitome 39.3-4.

 Other resources on line:

• Cleopatra III - Christopher Bennett's annotated Egyptian Royal Genealogy provides detailed references to sources.

• Cleopatra III - Jona Lendering outlines key events [Livius: Articles in Ancient History].

• Cleopatra III of Egypt - brief article in Wikipedia's web includes bas relief images.