Granny Weatherwax would recognise Mrs. Gurgle immediately, as she would Mrs. Gogol, or Evadne Cake or any Witch of another tradition, even if she didn't speak Morporkian or anything as close as English. Mrs. Gurgle has never seen a desert, but she knows the country between life and death. She's been and seen it and sent others and brought them back, too. Her world is water with little dots of land in it, and if she thought of a physical metaphor for the way to the hereafter, it would be under the sea.
She is one of the survivors of the Wave who reach Nation, an ancient, toothless, stooped and shrunken woman with gastrointestinal problems which provide Daphne's name for her.(1). The others who come with her, however, know her power and have great respect. When Mau is unconscious and floating between his world and Locaha's, Mrs. Gurgle brews a potion which sends Daphne to get him, rather like Tiffany Aching, but in the the time it takes a drop of water to fall a few feet onto her face.
(1)Her real name, or at least what she is called in the language of the islands, is Mar-isgala-egisaga-gol, which sounds rather like Gurgle, but more complicated.