I have to say something about Jill.
I think there’s two very precise reasons for her unpopularity.
The first is, how real and relatable she is. She behaves very natural, very much like a child in her situation would, and she feels very, very real. I’ve seen many posts by people who don’t like her who actually admit they relate to her, and I am sure there are far, far more who wouldn’t realise it. Not all the things Jill says or does are good, but all of them are absolutely plausible things for her to do, given her situation and background and age.
Jill’s nine years old in The Silver Chair. She went to the same school as Eustace and appears to have been raised by parents with a similar mindset as the Scrubbs, though while Eustace was pampered, Jill was encouraged to be more tough and active. She was raised without any religion or definitive moral compass (no, I do not mean that being brought up secularly meant being raised without morals; I am only talking about the context of Jill’s life)—her premise was, in short, pretty much the same as Eustace’s. And definitely different to the Pevensies’.
Which brings me to the second reason (these two blend in each other). Jill didn’t behaved perfectly, and she better—but she never behaved bad enough to undergo a significant change/redemption, nor did she behave well enough to be liked for just who she is.
When all Pevensies went to Narnia they already were, in a way, rooted there. Lucy had met Tumnus, Edmund had been enchanted by the witch, and Tumnus had been caught. The Pevensies met the Beavers, and they learnt of Aslan. They all were raised with a strong sense of duty, and Lucy was naturally faithful and open. Edmund behaved badly lately, and was then enchanted, but he received the same upbringing as his siblings. Peter and Susan were significantly older and more mature than any of the other children who went to Narnia.
Eustace was also only nine years old, and he behaved horridly, but he had his cousins, at least, and he grew immensely through his experiences in Narnia, while being led by others, and finally meeting Aslan.
But Jill? Jill had and knew nothing. A nine year old girl, bullied in a boarding school. Coming, most likely, from a similar background as Eustace, but still behaving much friendlier and nicer than him. (Actually, really friendly. Jill was a nice girl. People like to claim she wasn’t but that’s not true.) A boy she vaguely knew to be rather nasty all of a sudden told her of a magical world. They suddenly went there. She showed off, he fell down. She met a lion and couldn’t know who He was, yet after a while trusted him. She had to.
And later on? She trusted those who were nice to her, she was arrogant, she forgot things she ought to remember. She did all the little bad things that all the other children did, but they were not so dramatically bad and then redeemed as they were with Eustace and Edmund, nor were they simply accepted as every person’s right to not be perfect all the time, as with the other three Pevensies.
(I am not going to bring up Caspian, Shasta/Cor, and Aravis—children who were brought up in Narnia have an entire different set of things to their advantage or disadvantage.)
Jill is kind and courageous and plucky, but she has to navigate through Narnia with very little help—because Eustace can’t really help her, and all the Narnians who do (or don’t) are complete strangers to her, and she has to decide whether to trust them or not, and whether to agree with them or not, and she often decides wrong.
Lucy has a natural gut feeling about that, which isn’t unrealistic, because some children really have that. But I am sure that Lucy knew just as well who to trust back in England. Jill never really learned how and who to trust, and knew that people could be horribly cruel. But she was also a very small child with the natural desire and ability to trust. So, yes, she trusted the wrong people for the very shallow reasons that a child with no proper guidance has for trusting people. She also disagreed with people she deservedly trusted (like Puddleglum) for the natural shallow reasons that most children just can’t bear negativity or restraint too long.
She had no spiritual love for Narnia, not at first (though it developed greatly later on) and simply had to make her way through a strange landscape, without being granted the sense of magic and hope and special-ness that the Pevensies and even Eustace, had he accepted it from the beginning, were granted.
Jill was also whiny and, though never unfriendly or rude, odd-mannered and impatient. She was always supposed to be tough, and she was physically tough, but she was also emotionally sensitive, and very lonely. She had no friends, and she had a lot of fear, and absolutely no sense of home or safety. She cried several times in the book, which is an absolutely normal thing, even when one isn’t a child, even when one isn’t in a terribly dangerous situation, even when one isn’t constantly worried about one’s own decisions. And even though Lewis went so far as to excuse her for it, which shouldn’t even be necessary, there’s many posts on the internet saying how annoying she is for crying.
And her behaviour is typical for someone who is naturally friendly, but never learned proper manners, and who has a limited self-control; combined with that very certain air of someone who is used to being picked out to be the disliked one, not bullied for a certain thing but chosen because she was, in some way, particularly suitable for being a victim. Both the original “reason” as well as the… results of such don’t leave a person so quickly. They stuck with Jill and it shows.
But there’s another thing to Jill. A constant inner struggle. Not short moments of temptation, no a shocking experience to better her. From the very moment she steps into Narnia, until the moment she leaves, she thinks about what she does wrong, what she does right, with a great deal of denial thrown in—a denial she is often conscious of, and often not. A way from good but flawed, to, well good but flawed, though better, and more aware, and very willing to learn. A gradual, seemingly insignificant development, which began very early, and never really ended, and of which she was aware, and with which she didn’t really know what to do, and which she didn’t always want—until she understood, at least a bit.
And I think all this makes it so difficult to like her for many people. She’s incredibly human without being an obvious heroine, or even an anti-heroine, she is constantly developing, with interruptions and regressions, but with no clear redemption arc of any sort, never stops making mistakes, never stops learning from them; she behaves like a normal child would do in a difficult situation, and she has to face very specific difficulties under very specific conditions which, in that way, never happened to any of the other children.
And yet—she learned to love Narnia and Aslan so much. She spent years in England just to prepare herself for another visit to Narnia. She learnt nothing of (religious) faith in England, yet proceeded to believe in Aslan as much as she could, she kept a loyalty to Narnia and made friends with the other Friends of Narnia for years after her visit there, even though her connections to Narnia were the loosest of all the children, and she had to wait for her return much longer than any of them (not counting Digory and Polly, of course!). She never gained as much of the insight as the Pevensies and Eustace, and Digory and Polly, had, never really had a relationship to it that resembled theirs, but stuck to Narnia with all her strength.
And people hate her.