Mabel "Gammer" Peavey was a Witch mentioned at the Witches' Sabbat in Witches Abroad where the other witches in the coven were discussing the increasing shortage of witches.
She was one hundred and nineteen years old when she decided that she wanted to go mountain climbing. Gammer Beavis attempted to talk her out of it, but she wouldn't listen to her. Her last words were "Oh, bugger". It's the way she would want have wanted to go... at least according to Nanny Ogg.
Gammer is an old English term for a country woman.