The description of her death
in the book is quite 'fun'. Terry Pratchett
apparently thought of it some time before for the discworld
. However he couldn't use it because he didn't want to kill off Granny Weatherwax
(think what she might have done to him if he had tried).
If you are going to burn someone at the stake - first ensure that they have not filled their pockets with gunpowder and nails.