I don't know about the quest-related one (I think it was a named NPC) but the others do or should.
There is a quest related one. Found in a barrow at the foot of the mountain where Dagon's Shrine is. I believe...
I think it gives wisp wrapping as well.
I can buy more wisp wrapping than I find. I fight more bandit's dogs than I do wisp mothers.
It might've been an Ice Wraith. Those usually hang out with Wispmothers.
OP said witch so its probably human shaped. Ice wraiths are the ice snake things like the one at the Weynon Stones. What you are think of are wisps, or wisp apparitions I don't remember the exact term.