Rodan

Rodan was a female Time Lord who worked as a controller on Gallifrey. She helped to fight back an invasion of her homeworld by first the Vardans and then the Sontarans.

Profile
Her work involved maintaining the protective transduction barrier around her homeworld, monitoring threats to Gallifrey and reporting on it to her superiors.

Rodan befriended Leela, recently abandoned by the Doctor, who as a ploy, had pretended to collaborate with the invading Vardans. Both women were exiled by the Doctor outside the Capitol by him as part of the latter's ploy so that they could gather resistance to fight off the invaders. Rodan found such a natural environment hard to cope with mentally. After the Doctor had K-9 disable the transduction barrier and first the Vardans and then their masters the Sontarans invaded Gallifrey, she worked to restore it. (DW: The Invasion of Time)

Behind the scenes
Other than Susan Foreman, Rodan was the first female Gallifreyan seen on screen. Another Time Lady, Romana would join the the Doctor in his travels in the following season of the series.