Miss Eumenides Treason was a venerable old witch who took on Tiffany Aching as an apprentice three months prior to the events of Wintersmith. While a well respected witch, she was not well liked. She was unable to retain apprentices for long - Tiffany Aching being her last one. She was the subject of many eerie stories and rumours, most of which she started herself, which only serve to enhance her image as a force to be reckoned with. Miss Treason was known to be skilled at borrowing (using the eyes and ears of various animals) and she had the disconcerting habit of borrowing other people as a mirror by looking out of their eyes. This skill allowed her to compensate for going blind at 60 and deaf at 75 . She was noted to have used jackdaw, mice, owls and, near her death, two ravens that sat on her shoulders. There is no evidence that either of the ravens said "Nevermore". In her old age she used two sticks to walk and her broomstick has two smaller broomstick outriggers stuck on the back like training wheels. She could also speak Feegle.
All witches specialize in one or another field, and Miss Treason's specialty was Justice (in fact her name refers to the Eumenides of Greek Mythology, who came to represent Justice in later myths). People came to her to settle disputes, and usually found it very difficult to lie to her. The villagers said that kings and princes came for miles to ask her advice and seek justice from her. Regarded with awe and no small amount of fear by the local villagers, Miss Treason nevertheless had their great respect. She wore a heavy iron clock on her belt, which went clonk-clank instead of tick-tock. She could tell the time by feeling the clock hands. The locals believed her heart had stopped years before and that the clock was her replacement mechanical heart and she could not die as long as the clock kept going (likely a reference to the song "My Grandfather's Clock" which Pratchett used in previous works as well as to the heart of the Tin Man in the Wizard of Oz).
Miss Treason weaves the villagers' names into her cloth as she listens to their complaints. Miss Treason is blind, like the traditional images of Justice illustrated with her scale but Pratchett is also tying in the image of the Fates, Clotho, Lachesis, Atropos, who are usually depicted weaving at the loom. Clotho spun the thread of life, Lachesis measured its length and Atropos cut it off so it is not surprising that "The loom worried them (the villagers)."
She lived in a cottage in which everything in it was black, from the floor to the rafters. When Tiffany was her apprentice, she was required to paint her cheeses with black wax so that they would fit in with the theme. The cottage had all the hallmarks of an evil witch (skulls, spider-webs, etc.) which were all fake, bought from Boffo's, a joke shop in Ankh-Morpork. She coined the term 'Boffo' to describe the headology of creating an impression that you want others to see rather than what is really there. She used Boffo as a way of inspiring respect among the locals. Many of the apprentices before Tiffany found the whole thing far too creepy and left, usually within a day.
Miss Treason died during the events of Wintersmith, at the age of 111, though she gave her age as 113, worrying the former sounded a bit too cute. Since,like all witches, she knew the date and time of her death, she was able to enjoy her funeral ceremony the day before. Mindful of her image to the end, she used the presence of many of the local residents at her actual death to give them one last show, walking in to her grave surrounded by the villagers she had helped and guided over the years. Tiffany later half-jested that all the continuous visits by people to Miss Treason's grave would turn her into a goddess figure. By the end of Wintersmith this appeared to come to pass as, when Tiffany returned to the cottage, she saw that the villagers had been leaving pleas for help on and around Miss Treason's grave, in the hope that she could help them from the beyond. Her cottage passed to Annagramma Hawkin, who, after a decidedly shaky start, began to fulfill her role properly, with assistance from Tiffany and the Boffo's catalogue.
Miss Treason takes her given name from the Greek mythological figures the Eumenides also known as the Goddesses of Vengeance or the Furies. Combined with the surname Treason, it is a good name for a witch who wants to strike fear into the hearts of the locals.