Michelle appeared in 4 episodes of the BBC drama 'Merlin' as Nimueh.
Twenty years before Merlin arrived in Camelot, Nimueh was a High Priestess of thethe Old Religion. She and Gaius practiced magic together. She was friends also with King Uther Pendragon. Uther, desiring a son and heir, realised that Ygraine was incapable of providing one and asked Gaius to approach Nimueh with a request that she use the power over life and death to help his wife get pregnant. She did so, and as a result Arthur was born. However, according to her, a life had to be taken to restore the balance of the world in accordance with the laws of the Old Religion, and because of that Ygraine died in childbirth. Uther blamed magic in general and Nimueh in particular for her death and began the Great Purge, killing off hundreds of sorcerers and driving the surviving practitioners out of Camelot. While Gaius conformed to the New Religion, Nimueh was banished from the court, and vowed revenge for the death of all her friends .
The Mark of Nimuch (Air date: 28 June 2009) Nimueh exacted some measure of this revenge after Merlin began his apprenticeship with Gaius. She created an Afanc, a creature conjured of the elements of earth and water, with which she poisoned the water supply of Camelot. However, the plan was thwarted by Merlin, Arthur, and Morgana who destroyed the Afanc using the combined power of the elements fire and wind. Uther was dismayed when Gaius discovered a mark on the Afanc's egg that proved that the plague was Nimueh's handiwork .
The Poisoned Chalice (Air date: 28 June 2009) Nimueh swore revenge on Merlin for foiling her plan. Soon after that she posed as the handmaiden "Cara" within the court of Lord Bayard of Mercia. When Bayard travelled to Camelot to sign a peace treaty with Uther, Nimueh traveled with his retinue and traded out a chalice originally meant for Arthur with one that she had poisoned, and inveigled for Merlin to drink from it. She blamed the poisoning of the chalice on Bayard in order to sow discord and incite war, but the truth was discovered by Gaius before Camelot and Mercia could resume hostilities. She later led an unwitting Arthur to the caves under the Forest of Balor when he ventured to find the Mortaeus flower. She left him for dead as enormous spiders swarmed, but he was saved by a light sent by Merlin who knew he was in trouble .
Excalibur (Air date: 2 August 2009) Nimueh later attempted to kill Uther by reanimating his brother-in-law Tristan De Bois, who had sworn to return from the dead and avenge his sister's death, as a wraith. Ultimately, Uther wielded the sword Excalibur, which had been forged by Guinevere's father, taken by Merlin to The Great Dragon, and imbued with ancient magic for Arthur – to defeat Tristan. Infuriated by her defeat, Nimueh fled Camelot once again.
Le Morte d'Arthur (Air date: 23 August2009) When Arthur was bitten by the Questing Beast, Merlin travelled to the Isle of the Blessed and offered his life in exchange for Arthur's. Nimueh warned that such a trade would not be so simple; Arthur was brought back by water from The Cup of Life, but rather than sacrificing Merlin, his mother Hunith was taken instead, though Gaius attempted to sacrifice himself for Hunith to prevent Merlin from doing so. When Merlin returned, he found Gaius dead; Nimueh tried to convince him to join her, but he refused. The two battled and Merlin was hit by Nimueh's magic, which appeared to kill him. He survived, however, and summoned the power of the old magic to strike Nimueh with a lightning bolt, killing her, and using her death to save Gaius .