Heidi Scarlioni

Countess Scarlioni was the wife of Count Carlos Scarlioni who, unbeknownst to her, was a Jagaroth.

Biography
The Countess assisted Scarlioni in making preparations to steal the Mona Lisa, even going to the Louvre wearing a micromeson scanner to test its defences. However, while carrying this out, the scanner was stolen by the Fourth Doctor, an act she promptly reported to her husband, resulting in the arrest of both the Doctor and Romana.

The Countess was killed by her husband shortly after he revealed his true alien origin to her. (TV: City of Death)