It seems I was actually right about the old woman. She spacifically said that she used to be OUTSIDE WANO. Which basically means it's likely she sailed as a pirate. Meaning, that old hag was part of the Rox, which simply explains why she was able to turn into Shiki's face, because it's likely that she touched Shiki during her time in the Rox pirates.
I can speculate that she was the Ace card in beast pirates, and she accompanied Kaido. And I can also speculate that se was part in setting up Oden when he came back to Wano, and she took part in screwing Oden because of her tricky ability. However, I can also have a big feeling that she died by Oden, and was cut down, which explains why her ability is now with Bon Clay, because she simply is dead now.
Things are getting connected in my book