Sienna Fowler grew up in South Carolina, where she took advantage of her sex appeal to gain insight into her targets. The story behind Sienna's codename originates from her "wild" parties she organized for businessmen and officials in her youth. The reason for this was to record incriminating behavior and information, which would then be sold to those wishing to blackmail or discredit them.
After she managed to dupe the US Federal Government's top surveillance expert at one of her parties, she was offered a job. How she became a sniper is unknown.