Diome, Witch of the Night

Diome, Witch of the Night appears in Eric, where she is in the company of the adventuresses Herrena the Henna-Haired Harridan and Red Scharron for some girl talk and a game of canasta.

She only appears this once in the chronicles in a non-speaking part, and it is possible she is just there to make up the numbers for the canasta. The girl-talk, the cards, and the consumption of sweet sticky drinks in small glasses, are interrupted when Discworld reality intersects with the Dungeon Dimensions for just long enough for a disembodied voice to be heard shrieking ohshitohshitohshitI'mgoing to die!, Doppler-shifting from one end of the bar to the other. This is accompanied by the bizarre scampering of many tiny feet.

Just one of those things in a city with a high level of background magic...

It is also highly possible that Diome is not an accredited witch, as given what Granny Weatherwax is capable of in a competitive card game, people might think twice about dealing her in more than once. Plus, if you imagine what Granny might say if she'd heard that a witch was calling herself a Witch of the Night, I doubt she's a real one...