The Abbess (Eye of the Gorgon)

The Abbess was originally a human. Possessed by Gorgons, she served as their host on Earth for  hundreds of years. She wanted to bring the rest of the Gorgons to Earth using a portal which resembled a well. She was turned to stone when Sarah Jane Smith used a mirror to reflect the Gorgon's power back on itself. (SJA: Eye of the Gorgon)