Shannon O'Donnel was a Human woman born in the year 1958 who lived during the 20th and 21st centuries on Earth. She was a distant ancestor of Starfleet Admiral Edward Janeway and his daughters Kathryn and Phoebe. Kathryn Janeway looked at O'Donnel (or rather, the romanticized tale of O'Donnel passed down through family stories) as a role model.
O'Donnel was a trained engineer and an applicant to NASA's astronaut program. In 1984, she started work at the top secret US Air Force Flight Test Center at Groom Lake, Nevada (colloquially known as "Area 51") under Jeffrey Carlson. Doctor Carlson was continuing his life's work: attempting to decipher the operating principles of an alien spaceship which had crashed near Roswell, New Mexico in July 1947. (TOS novel: The Rise and Fall of Khan Noonien Singh, Volume 1, DS9 episode: "Little Green Men")
In 1986, Project F (as Carlson's operation was known) had a burst of activity after Naval Intelligence gave them several devices recovered from an intruder captured aboard the aircraft carrier the USS Enterprise while it was docked at Alameda Naval Base. However, before they conducted more than a cursory examination of the devices, O'Donnel encountered a mysterious woman who somehow got past Groom Lake's intense security. After a brief standoff, O'Donnel was somehow tranquilized, and after she regained her senses the woman and the devices were gone. (TOS novel: The Rise and Fall of Khan Noonien Singh, Volume 1)
By the 1990s decade, O'Donnel was working on the top secret project to develop the DY-100 sleeper ship, working with people such as Doctor Marcus Walter Nichols and pilot Shaun Geoffrey Christopher. Roberta Lincoln also provided technical assistance, giving O'Donnel access to technological specifications to help complete the ship. Once the unnamed ship was completed, Lincoln and O'Donnel launched the ship. As instructed, O'Donnel later claimed that she was under Ferengi mind control at the time when questioned about the incident. While no charges were brought up against her, O'Donnel did lose her position at the government lab. When Gary Seven retired, Lincoln took over for Seven, and briefly considered bringing in O'Donnel as her assistant before ultimately choosing Rain Robinson. (TOS novel: The Rise and Fall of Khan Noonien Singh, Volume 2)
In late 2000, O'Donnel convinced Henry Janeway to drop his opposition to the construction of the Millennium Gate in Portage, Indiana, and to close down his bookstore to help make room for the project. The pair fell in love and were married. By the 2050s, they had numerous children, grandchildren and great-grandchildren. A photo was taken at this time, which the crew of the USS Voyager discovered and gave to Kathryn Janeway as a gift in 2375. (VOY episode: "11:59")
In an alternate timeline in which Khan Noonien Singh was victorious in the Eugenics Wars, O'Donnel, Shaun Geoffrey Christopher, Rain Robinson and about 100 of Earth's top scientific minds launched the SS Botany Bay in November 2010. Their intention was to escape the horrors of Khan's conquests and settle a habitable planet in the Eta Cassiopeiae star system. Unfortunately, the ship went off course and was eventually discovered in June 2376 by Princeps Julian Bashir of the Khanate of Earth starship Defiance. O'Donnel and the rest of the crew of the Botany Bay learned that Khan had forced Earth's entire population to undergo genetic engineering and had gone on to create a brutal and despotic interstellar empire known as the Khanate of Earth. (Myriad Universes novel: Seeds of Dissent)