Interesting theory! I suppose it's a possibility, although unless we ever see the script for the proposed movie, we'll never know if those were the lines they were thinking along.

We do know they were apparently trying to turn SC into a "girl power" action movie, which was what led the Lewis Estate to drop it. It certainly gives one the impression that they really didn't "get" what the original story is about or what Narnia as a whole is meant to be like, so I have zero regrets that this particular production never got off the ground.

That said, I would also add — respectfully — that I wouldn't be a supporter of the idea you've proposed, if it was what the film was aiming for. It's just too much like what MGM did with The Wizard of Oz in the classic 1939 film, in which nearly all the characters Dorothy meets in Oz are doubles of people she knows in her everyday life, and she wakes up at the end to find that her adventure in Oz was something she dreamed after being hit on the head by the window frame during the cyclone. In the original book by L. Frank Baum, Oz is definitely a real place that Dorothy travels to and returns from, and not just a projection of her own inner hopes and fears and so on.

That's what I would hate to see done with Narnia, in any adaptation of any of the books — an implication that Narnia is somehow a projection of the child characters' own feelings and struggles, a reflection of their psyche, rather than a real world separate from ours that exists in its own right. I've seen hints of the former approach in a stage adaptation of LWW as well, which seemed to be making out that the White Witch's occupation of Narnia and the Narnians' resistance against her were directly parallel to the war that the children are experiencing in their own world. Whereas in reality — I mean, in the book — Lewis uses the war solely as an excuse to get the children into the Professor's house and never refers to it again, even implicitly. If a film-maker was trying to do something similar with SC — take the bullying scene that opens it and make the entire story all about that — I'd say that's seriously missing the mark. Again, if that's anything like what they were planning to do, I'm relieved that adaptation never went ahead. 

A friend did a writing exercise from SC, with Jill being shut in a dark cupboard by 'Them' - the bullies-  who knew about her claustrophobia (which she tells about in the Underworld chapter).

(Later she sympathises with some of the Earthmen who are similarly bullied by a different 'Them', the witch's overseers) 

For reference in the discussion, the original quote from TriStar Pictures President Hannah Minghella was:

"Silver Chair is a perfect moment to rejoin the franchise because it introduces a new character, a young girl named Jill, going into Narnia for the first time.

Thematically, the story of a young girl who is being bullied but who has to find the courage to stand up not just for herself but ultimately all Narnians has such strong positive messaging."

https://www.narniaweb.com/2017/06/the-silver-chair-is-about-a-bullied-girl-says-tristar-president/

I don't think any of that description is necessarily a divergence from the book, though I guess it depends how much you read into the word "thematically" and how much nuance you expect from a senior studio executive

To be honest, I'd reasonably expect most interpretations of the book to describe Jill Pole's character arc along similar terms... Afterall, it's not just an incidental detail that the opening scene is of her being bullied at school.

@courtenay I agree with your concerns but FWIW, I'm not sure having the same actor play the LOTGK and the leader of the bullies would have necessitated implying Narnia was a dream. In the theater, they will sometimes have thematically similar characters be played by the same member of the cast. That being said, it is probably something that works better onstage than on the screen and I wouldn't recommend it in part for the reasons you cite.