Natasha Stengos was a member of a group of people who tried to free their loved ones from the suspended animation chambers of Tranquil Repose on Necros.
With her friend Grigory she broke into TR and tried to take back her father, Arthur Stengos. She found he was replaced with a mannequin and later found him in a laboratory being turned into a Dalek by the Great Healer (Davros). She couldn't stand looking at him like that and killed him when he asked her to.
She and Grigory were then captured by security and interrogated by Takis and Lilt (who wanted to mark her for the guards she killed). The Sixth Doctor later freed her and Grigory and they showed him where Stengos was. The Doctor wanted them to destroy the lab and then meet him in reception.
They tried to destroy the incubators mutating human brains into Daleks but were stopped when a Dalek appeared hovering above them. She tried to escape with Grigory but both of them were exterminated by the Dalek before it self-destructed. (TV: Revelation of the Daleks)