Like mostly theories about Kubrick films, it's a reach that tells you a lot about the person who came up with the "theory".

Not to say that Kubrick films don't have themes and subtext and all of that, but one must remember that one of the things Kubrick was criticized for in adapting Stephen King's novel was doubling down on making Jack Torrance the bad guy. I haven't read the book, but from what I'm told, in the film he comes across as much crazier, and it begins earlier, and the character is less sympathetic.

No, I think the Wendy theory is bunk and there are already videos out there addressing, in detail, why it doesn't make sense.