Ezakra: Based on WoJ that we need to look in Celtic lore for the staff, I'm betting MW holds mantles/masks of both Baba Yaga (Russian) and the Cailleach (Celtic), as they are often compared by scholars of mythology anyway and their mythsseem to have borrowed from each other.

Then again, I've been thinking that WoJ only says we can find out how the WC got the blackstaff by looking in Celtic lore in 1065. This does not necessarily mean that this is when MW lost her walkingstick. Could be that she lost it to Arthur/Merlin, it was passed down through Arthur's (supposed) line, and the WC got hold of it in one of the weapons raids pre battle of Hastings.

Lastly, putting in my 2 cents on a few things:
Just because she now wants it back does not mean MW did not orchestrate it being passed to wizards in the first place.
The heist won't be getting the staff back. I think we'll see it again/learn more about it before MW gets it back.

Not sure how reliable, but here's another possibility

Cailleac Bhuer (call-y'ac V'fhoor) - Also called the Blue Hag or Stone Woman. She originates in Scotland and is an old woman of human size who walks by night with a walking stick made of holly with the carved head of a crow on top. A large carrion crow sits on her left shoulder and a touch from her magical staff means instant death to a human. If her staff is found unattended it will give its owner the power of enchantment.

I'm trying to hunt down a story of it being left unattended