She was member of the Committee of Three, together with Lord Provost Tepesh and Arata. As members of the Arcalian House, Tepesh and Ouida were Gallifreyan, and were known to Rassilon personally. However, they were also Vampires (secretly, presumably) and plotted against him. It is implied that they killed the third member of the Committee of Three before meeting with the Great Mother and Cassandra from the Sisterhood of Karn, plotting to destroy Rassilon's Foundry. They were killed by the automated sterilisation of the Foundry.
While dealing with the aftermath of the explosion of anti-time, the TARDIS created a series of holographic projections, taken partly from reality and partly from the memories of the Eighth Doctor, his companion Charley Pollard and the TARDIS itself. One such projection was the meeting in Rassilon's Foundry as the TARDIS was looking for information on the Divergence. Inside this projection, it placed Charley in the role of Rassilon and itself in the role of the Great Vampire Arata. The projection of Ouida was created using the image of the Sixth Doctor's companion Peri Brown. (AUDIO: Zagreus)