Sinead Starling was the female Starling triplet.
Sinead was born with Ned and Ted, and was the only girl of the three. She was a patron at Cahill manor for Grace Cahills week-long winter holiday. After she died, Sinead went to her funeral with her brothers, putting a shovel of dirt in Grace's grave. The Starlings got to go to the will reading, and a video played by William McIntyre showed Grace offering one million dollars or to hunt for the 39 Clues. The Starlings joined the hunt, saw the clue card, and put their heads together, then leaving. Later they tailed Amy Cahill, and Dan Cahill, but then Nellie Gomez drove the car straight off an exit ramp, leaving Sinead gawking.
However, they were able to track them down to the Science Museum and Sinead took a photo of the lead to the clue in Franklin's letter that Dan saw with the black light. The black light reader was snatched away from them, and Sinead said they'd get a half-hour head start or Ned and Ted would hurt them. As the Starlings turned to leave, Amy and Dan tried to warn them of The Man in Black, but Sinead didn't believe them. They walked out the archway and it blew up, crushing the Starlings. Sinead survived and was taken to a hospital to recover. It will take months for the Starlings to recover.