Granny would become a new GHW in the future
Not immediately, but after they return to Norway and conquer the castle. Then, she would lead the two species to co-exist.
I know that in the end the unnamed protagonist (this is for the book, I've never seen the movie) is still a mouse, but this is wild. Perhaps becoming a human again made him a crazy old man. This could explain his ability to communicate with the mice. And of course, his childhood dream was to have his very own Mouse Circus. Also, if you merged the universes,
the Other Mother could totally be a Real Witch.
The Grand High Witch's "frying" powers are the same as
Matilda's telekinesis.
The Grand High Witch was very clever from birth but, like Matilda, left her brain power unused and began to be able to spring rays from her eyes, like Matilda. The GHW, however, was never placed in an environment where she could use her mental capacities, and she kept her power, bettering with time until she could not only merely push or hold things from the distance, but even burn them.
The woman with the green snake wasn't a witch at all.
The boy never saw her again, so for all we know, she wasn't at the meeting. And seeing as it was winter and many ladies were wearing gloves, she could well have been a human. Her intentions, if she was a human, are unknown. She could have still been malicious (a child molester, wanting to kidnap him for money, the list goes on), or she could have just been a rather
eccentric woman who
really did just want him to look at
her tame snake. She could also have been trying to prank him, having heard of witches herself.
The events of the book and both of its film adaptations take place in a
Shared Universe.
By in-universe chronology,
The Witches (2020) is the first one. In it, the witches are extremely badass at magic — they cause Grandma's cough, the Grand High Witch is able to levitate etc.; in particular, the GHW maintains her beauty with sorcery rather than with
Latex Perfection.
Fast-forward to in-universe 1983, when the book's events unfold. The current GHW already has to wear a mask and is a much less impressive sorceress. More than a decade of witch-hunting has clearly paid off: the witches aren't gone (probably they reproduce by some magical means, given they are a One-Gender Race), but they are getting weaker.
Finally, 1990. The GHW is struggling with her disguise so much that she forgets her own fake society's name and just trying to say "children" makes her grimace (she is lucky Mr. Jenkins, to whom she is talking, isn't the sharpest knife in the drawer). Despite recognizing Grandma as a witch hunter, she does nothing to her except meddle with her food, which Grandma discovers immediately. The witches' organization is crumbling down, and the rats are deserting the sinking ship — hence Susan Irvine's redemption.
No, characters from the 1960s and from 1983 didn't exterminate the witches outright – but they made their magical power dwindle.
