Lauren MacMillan was Navigational Officer aboard the Hydrax. A human who fell into E-Space through a CVE, Lauren assumed the name Camilla as one of the Three Who Rule. She was the consort of Zargo, the ship's former captain.
The Hydrax crossed from N-Space into E-Space, where the crew found a primitive planet. Turned into vampires by the Great Vampire, they controlled the natives for a thousand years until the arrival of the Fourth Doctor, who killed the Great Vampire and the Three Who Rule. She aged, decayed and crumbled into dust. (TV: State of Decay)
Behind the scenes
Carmilla is the name of a 1872 famous vampire novel by Joseph Thomas Sheridan Le Fanu.