Larna

Larna was one of the Doctor's best students at the Academy when he taught on Gallifrey.

Biography
Larna developed a friendship with the Doctor during her time at the Academy, where she learned from the High Council a prophecy about Gallifrey falling after a number of attacks from different species. To try and stop the Doctor leaving for the Station, she commited suicide with a knife, but she was resurrected by Omega at the Doctor's request. Larna set off to tidy up the “side-effects” from the Effect, which had caused history to change. (PROSE: The Infinity Doctors)

Larna travelled to the Shoal in Gallifrey's past, where she began monitoring a cicatrix in time and sent information back to Gallifrey. During this time she met Marnal, a Time Lord who had been sent to destroy the Shoal, as well as Ulysses, Penelope Gate, and Saldaamir. She told them that she was from their planet's future and told them the prophecy that told of Gallifrey falling after a number of attacks from different species. A single Time Lord would have a hand in all of those events and he would find the Lost Scrolls of Rassilon and lead Gallifrey from darkness. (PROSE: The Gallifrey Chronicles)

Larna worked for Daniel Joyce in Berkeley, San Francisco in 2002 on the Advanced Research Project. (PROSE: Unnatural History)

Larna was referenced as "a young woman with long blonde hair in an extraordinary piece of haute couture" in a list of the four Time Lords who had survived the War. (PROSE: The Gallifrey Chronicles)

Behind the scenes
Larna's name appears to be a reference to "Lady Larn", the name given to Susan before her travels with the Doctor in Eric Saward's story Birth of a Renegade, published in the Radio Times Doctor Who 20th Anniversary Special.