User blog comment:Ḡwẵine Ḹٍٍkƨ Ĺiĸe Ͼềлȑềd/Revival of the Witch???/@comment-1948423-20111016165614

Nimueh was killed by Merlin. And in the first episode of the fourth series, which was called "Revival of the Witch" when it is actually called "The Darkest Hour". It is mentioned to Morgana as powerful witch.