She was not chosen.
Sonohara Fi was a worker at the Republic Senate. After witnissing the Chancellor slay a Jedi that survived Order 66 in his office, Sonohara was hunted down by the Stormtrooper army. She managed to escape on a speederbike and find Senator Bail Organa who was just leaving Coruscant and was allowed on board. Ever since then, Organa had provided her a home on Alderaan and a job at his side. When Princess Leia was captured by the Empire Sonohara left Alderaan to find what happend the princess. A few days later when she returned to her planet, it was gone!
Sonohara had recieved some coordinates from Bail Organa before the planet blew up and followed those to Yavin 4 where she was taken into care of The Fire Skeleton and quickly became part of the Rebel Alliance.