Her real name is Lucy Tockley, but she chose Diamanda because it sounded more witchy. She was born in Lancre, but went away to school, and returned while the Lancre Coven were touring the Disc in Witches Abroad. Seizing an opportunity to fill the vacancy, she set up her own coven, insisting that the Wisdom of the Ancients was more significant than anything a lot of old people knew. How much natural witchiness or common sense she actually had may be illustrated by her willingness to summon the sadistic and evil elves. It is undetermined whether she is a natural witch or whether her magic in fact comes from the Elf queen. At the end of Lords and Ladies, Granny speculated Diamanda might have been having a relationship with the young wizard Ponder Stibbons, but he returned to Unseen University before the relationship, if any, could be established.

In Lords and Ladies, Diamanda duelled Granny Weatherwax, the challenge being to look directly at the sun for as long as either could bear it. When Nanny Ogg realized that Granny would lose the duel, so she enticed her grandson, Pewsey Ogg, to run across the magic circle in which the duel was taking place. Crossing the circle caused Pewsey to cry out and Granny to look away from the sun, get up and return Pewsey to his grandmother. So while Diamanda was the technical winner of the duel, the crowd considered Granny the best witch, because witches are supposed to help young boys who cry instead of being selfish and only thinking of themselves. Diamanda does not appear after Lords and Ladies.

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