Thana

 was part of the orchestra on board the Apocalypse Deathwatch.

She found the Nine in the Vault stealing some of the rarest artefacts. The Nine attempted to kill her, but she couldn't die as it wasn't from natural causes. She shared his interest in the rare and wanted to join him in his travels. She told the Fifth Doctor and Jenny that people on the ship were thrill-seekers and wanted to see the specticle. (AUDIO: Relative Dimensions)