As part of an Orion operation to dominate the sector that contained Treva and prevent the planet from joining the Federation, Nalavia was surgically altered to appear Trevan. Her green skin was bleached to a pale shade, and her distinctive blue eyes were changed to a shade of green, though this had the effect of making them appear slightly unnatural. She remained very beautiful and seductive and had black hair.
- As Nalavia is undercover as a Trevan, it is possible that "Nalavia" is not an Orion name, but a Trevan one.
Nalavia came to Treva and created a false identity for herself, including altering birth and school records, in which she purported to have been born on a farm in a remote part of the Trevan frontier. She entered politics and circa 2355 was elected to Treva's Legislative Council. She was a popular leader, and was soon elected president, a position she held for five Trevan years. Once elected, she began consolidating her power, tightening her grip over the Trevan people, and deconstructing Trevan democracy, steadily building her power into that of a dictatorship. Nalavia seduced and bribed the other councilors to follow her wishes.
- Nalavia's popularity, influence, and swift rise to power may be due to the dominating effects of Orion pheromones as in the ENT episode: "Bound" and other sources.
Nalavia and several members of her cabinet were the majority shareholders in companies manufacturing the drug Riatine, which they labeled a water purifier and distributed to the water supplies of Treva's four major cities. The drug suppressed Trevans' emotions, reduced their independence, and made them suggestible to government propaganda. Nalavia made intoxicating drugs cheap and widely available to filled their emotional voids.
In response to Nalavia's tyranny, Lord Rikan launched a rebellion, aided by the famous mercenary group of Adrian Dareau. When Aurora pretended to be a free trader and flirt with the councilors to turn the Legislative Council against itself, Nalavia quickly implemented trade restrictions to drive off the competition. To discredit the rebellion, Nalavia had her own soldiers commit terrorism in disguise.
Although Nalavia had previously told the Trevans that the Federation was a cruel empire that would gut Treva, in 2364 she contacted the USS Enterprise, begging military aid to put a stop to the insurrection so that it could join the Federation. Lieutenant Commander Data and Lieutenant Tasha Yar were sent to investigate affairs on Treva and met with Nalavia at the Presidential Palace. Again, she begged Starfleet's assistance, an attack from space on Rikan's castle of Warrior's Rest, in exchange for their membership of the Federation. In fact, she planned to hold Data and Yar hostage to force Starfleet to act: whether to attack Rikan's rebels as demanded or attack Nalavia's government to rescue them. Either way could be construed as a violation of their Prime Directive and show the Federation as a hypocritical, making other worlds in the sector reluctant to join.
However, Yar was kidnapped by Dareau's men and brought to Warrior's Rest. Nalavia covered for her disappearance by claiming she was on an agricultural tour of the Trevan dairy industry, and continued showing Data around the capital city, meeting with survivors of the terrorist attacks and visiting schools. The two flirted together during their meetings, before Dala also escaped and headed to Warrior's Rest in search of Yar.
When Yar was allowed to send a message to the Enterprise, Nalavia believed that the Starfleet officers had gone over to the rebel side. She ordered a major military assault on Warrior's Rest, going all out to kill them in the effort. However, her soldiers were recalled to the cities to help quell uprisings of people now free of the effects of Riatine. A full-scale civil war broke out. Data was able to extract unaltered records from Trevan computers and show how Nalavia's identity had been falsified. The information was broadcast to the Trevan people, who marched on the Presidential Palace in fury. Nalavia promptly surrendered to Starfleet and was proven to be an Orion in the Enterprise sickbay.
The Enterprise brought Nalavia to Starbase 68 to be transferred into Starfleet custody. However, it was expected that she would only be confined in some comfort before being returned to the Orions, as part of a prisoner exchange for Federation citizens captured as slaves.