Harriet was a crewmember aboard the Teselecta.
She was apparently part of the Teselecta's art department, which helped make the Teselecta look identical to whoever it was copying. During the mission to punish the Nazi leader Adolf Hitler by posing as a Nazi officer named Erich Zimmerman, Harriet insisted on getting a good look at the subject they were copying, as the Teselecta had made Rasputin green when the crew had relied on the ship's sensors alone. (TV: Let's Kill Hitler)