Who is Qiwi Linsolet from A Deepness in the Sky and what is their importance?

Eight-year-old, Qiwi Linsolet, is a member of the Qeng Ho. By the time they arrive on the On/Off Star, she is fourteen. Qiwi is described as a brilliant, young woman, and she soon becomes Thomas's constant companion. She later learns that Thomas Nau murdered her mother, and she kills him.