The witch could also be an alternative Vamirio from a future where they failed in some way or another. Maybe they never got off the island, maybe Helck turned on them, or the humans simply got too powerful to stop and steamrolled the planet. The look she gave Helck when they met wasn't a particularly kind one. Felt more like wary assessment.
If we have massive teleportation magic and god-tier resurrection and awakening magic, who's to say we don't have time magic? Vamiro is the most powerful of the four, and she's expected to only get stronger.
Then she just parked herself on the island to make sure they wouldn't fail on a second go-around.
The resemblance is far too close to easily dismiss a "future Vamiro" theory.