After she met the Ninth Doctor, he told her that she was "sweet" and asked her to join him on his travels. Lynda agreed and, along with Jack Harkness, they set out to save Rose Tyler from her "death" during The Weakest Link. Lynda was horrified when Rose was seemingly disintegrated. After escaping capture, Jack used a supposed disintegration beam on Lynda to show the Doctor that it was in fact a transmat and Rose was alive. (TV: Bad Wolf)
In the battle against the massive Dalek invasion, she acted as a coordinator by using the sensors to track Dalek movement. This ended when the Daleks located her. She reported to the Doctor, and he assured her that that side of the station was reinforced against meteors. The Daleks began to cut through the door with a torch as Lynda watched. This proved unsuccessful. Five Daleks rose outside the observation window. Upon noticing Lynda, the luminosity dischargers on its head flashed in tune to the word "exterminate" (its voice unable to be heard in space), then the Dalek shot the glass, exposing Lynda to the vacuum of space, killing her. The Doctor heard her scream over the communication system. (TV: The Parting of the Ways)
Lynda was a very bright, bubbly, cheerful person. She became fast friends with the Doctor, who agreed to let her accompany him when she requested to do so. She was very concerned about what the audience thought of her, asking the Doctor if viewers of Big Brother on Earth liked her. He absentmindedly said that people thought that she was sweet.
She showed loyalty to and great trust in the Doctor, despite only having known him for a few hours. She stuck by his side assisting him even when she was told to get to safety. She had faith that he would keep her safe and fulfil his promise to take her on the TARDIS with him. (TV: Bad Wolf / The Parting of the Ways)