Petra was the first member of Salamander Army that Ender Wiggin met when he was moved out of his launch group and assigned there. As with many others before and after him, he initially mistook her for a boy. Her being a girl drew unwelcome attention to her throughout her military career, and she was not particularly popular with the rest of Salamander Army. She did, however, offer to give Ender some extra training, and taught Ender how to use his Flash Pistol to shoot, along with several other Battle Room maneuvers, which he had not been able to master during his abbreviated stay with his launch group. This drew the ire of Bonzo Madrid, the commander of Salamander Army, who hated Ender. Petra eventually became the commander of Phoenix Army. As tensions between Bonzo and Ender escalated, Petra tried to instigate a fight between Ender and Bonzo's thugs by slowing him down in the hallway. She figured that she and Ender, who were trained in hand-to-hand combat, could take on the attackers in the narrow hallway, rough them up enough to get the fight out of them, and then the tensions would be gone. Instead, Bean, misunderstanding Petra's intent, summoned Dragon and Rabbit Army to escort Ender safely back to his barracks. Several days later, Bonzo cornered Ender in the showers, resulting in the fight that cost Bonzo his life.
After this, Petra and several others close to Ender were graduated to Command School to be his squadron leaders while he commanded the human invasion fleet. When the jeesh was moved to Eros to begin the actual battles against the Formics, Petra was given her own small room off from the other boys' barracks. Ender relied most on Petra during the battles on Eros. Although Ender didn't seem to notice, Bean remarked that this was taking a heavy toll on Petra, as her perfectionism lead her to berate herself for every mistake. Finally, Petra cracked and fell asleep during a battle, causing heavy losses to her troops; her entire army would have been wiped out had Bean not noticed her inattention. After that, Ender stopped depending on her so heavily and Petra lost most of her truculence. During the final battle above the Formic Homeworld, Petra's troops provided a screen for the others as they raced 'down' toward the planet, attempting to set off the Molecular Disruption Device and destroy the world. Immediately following this battle, when the children were told that they had actually destroyed the Formics, Petra was the first to feel horror, for the lives of the humans that had been lost and the extinction of the Formic species; she began crying and several others followed suit. Between Eros and the return to their respective homes, there was a brief period where the jeesh, minus Ender, were able to spend time together. At that time, Petra and Bean became close, to Dink Meeker's chagrin. He accused Petra of having feelings for Bean, but she felt their relationship was "something else."
After the war, she returned to Earth and settled back with her parents and brothers Stefan and the infant David, trying to live a normal life. She re-learned Armenian and picked up the slang; in school, math was far too easy but literature and gym classes provided a challenge. She was popular for a few weeks, but after the 'popular girls' lost interest in her, she hung out with the 'social rejects,' a cause of concern for her principal.
A few months later, she was kidnapped by Achilles de Flandres along with the other members of Ender's Jeesh except for Bean, whom Achilles attempted to kill. The ten captives were put in isolation, where Petra was the last one to break after five weeks. During their imprisonment, she designed a dragon logo with an encrypted message designed for Bean, which was sent as a chain letter along the email network. Bean eventually found and decoded the message as intended. He informed Peter Wiggin, then only known as Locke, who managed to get all the children but Petra rescued. Achilles personally interfered with Petra's rescue, killing her two escorts in front of her. He informed Petra that, since Petra's dragon graphic was the only thing for which Achilles couldn't account, he had deduced that she had engineered the escape and therefore had 'won his contest'.
Achilles and Petra flew to India; midflight, Achilles opened the airplane door and ordered Petra to close it while he held her by the arm. Petra contemplated trying to hurl the two of them out of the plane, but decided against it, as it would have been too easy for Achilles to simply let go and let her fall alone.
Petra was put under constant surveillance and given no internet access in a compound with the rest of India's Battle School graduates. Whereas the other graduates devised a campaign against Thailand relying on India's massive armies, Petra, confident that the threat of Pakistan in the West would render an Eastern war impossible, designed a brilliant campaign of small, mobile platoons who wouldn't need supply lines. However, Achilles managed to broker a peace between India and Pakistan; nevertheless, he did not use Petra's plan.
Meanwhile, Bean had been leaving messages for Petra on military forums, alluding to her as Briseis and himself as Hector. Petra helped Virlomi, another Battle School prisoner, respond to Bean, but Achilles discovered them. He summoned Petra to his quarters and threatened to kill Virlomi; he struck Petra, and she retaliated, knocking him to the ground and nearly incapacitating him. Before Petra could kill him--or even thought to kill him--Achilles drew a gun. Petra, in response to the madness in Achilles' eyes as he glared at her, pretended to have been won over by Achilles in his defeat, saying that she liked men who were confident enough not to feel threatened by her. She kissed him and then he sent her away. Meanwhile Virlomi escaped on her own.
Eventually, Bean and Suriyawong lead Bean's division of expertly trained Thai troops to India to rescue Petra. Achilles, cornered before he could reach transportation out of the base, forced a stalemate by putting a gun to Petra's head. She tried to signal to Bean that he should shoot Achilles anyway, but a Chinese officer, whose troops were also attacking India in response to the country's Eastern campaigns, incapacitated Achilles. As per the deal that Bean and the officer struck, Bean let the Chinese fly away with Achilles alive, even though Petra seemed tempted to kill him herself.
Petra's family moved to Ribeirão Preto, where Peter Wiggin had set up his compound as the newly-elected Hegemon. For three years, Petra and Bean traveled around the globe, avoiding Achilles. During this time, Petra, having discovered Bean's genetic predicament, became determined to marry him and bear his children. Bean persisted in ignoring his reciprocation of her feelings until the two visited Anton; the elderly scientist convinced him, and Bean agreed to have children only if there was a way to be sure that Anton's Key was not turned in the babies. The two were married in an Armenian Catholic ceremony shortly thereafter.
Bean and Petra located Volescu, Bean's half-uncle and the scientist who had worked on the Anton's Key project to help them with in-vitro fertilization. Petra deduced that Volescu did not have a test to determine in which of their nine embryos Anton's Key was turned, but, afraid that Bean would then refuse to have children, did not tell him. One embryo was implanted in Petra and the rest were frozen and placed in storage, but Achilles soon stole them and, unbeknownst to Petra and Bean, implanted the eight embryos in host mothers.
Leaving a very pregnant Petra in Damascus with Alai, Bean flew to Ribeirão Preto, where Achilles had taken over Peter's compound. He and Peter faced Achilles, and with the help of Suriyawong, Bean managed to kill Achilles.
Bean was now well over six feet tall; he was projected to only have a handful of years left so, as he and Petra searched for their remaining children, Graff suggested that Bean go on a prolonged relativistic voyage with all of his children who had Anton's Key activated in them, in hopes of having his children and himself stay alive long enough in hopes that someone might discover a cure in the interval. Petra said that she would never forgive him if he were to go, but Mazer Rackham secretly helped Bean divorce Petra just before he faked his death in Armenia and flew into space.
Petra remained on Earth as the general of the Hegemon's forces; her five children with Bean remained in Ribeirão Preto with her mother, where Peter visited them nearly every day. Over a year after Bean's departure, Petra finally was forced to return home, where she discovered a letter that Bean had left her beneath one of their children. Unable to face it, she asked Peter to read it to her.
Later, Petra married Peter and had five children with him. She outlived Peter and was forced to once again say goodbye to another great man in her life.
Over 50 years after he left Earth, Ender Wiggin sent a message to Petra over Ansible, telling her that he had found her last missing child, Arkanian Delphiki on the planet Ganges.