Also I skimmed to the passage in question. I think you should keep in mind that Rey overcomes her core belief WHEN the Jedi of the past encourage her to defeat Palpatine regardless of how weak she is in comparison to him after her life force was drained. Because Luke convinces her that she’s still valuable and can still do the right thing regardless of her heritage.
Below is my interpretation of Rey’s TRoS arc, for you to reference, similarly to when I showed you my interpretation of her TLJ arc a while back.
Her character arc in The Rise of Skywalker starts off with her receiving a vision of herself as a Sith, ruling on the Sith throne — she begins to fear the mere idea of her turning to the dark side, convinced that no one is going to give her approval if she were to turn to the dark side; hence why she begins to feel unworthy of being a Jedi and using a lightsaber, convinced she would become a Sith if she remains a Jedi and continues using a lightsaber.
Of course, Rey learns of a truth even worse than that of her parents throwing her away like garbage… she is Palpatine’s granddaughter — she begins to fear of what the wider galaxy would think of her if they find out who she is, since her grandfather is the Sith lord who not only destroyed the Jedi Order but also made the galaxy suffer under the rule of the Galactic Empire and was also responsible for the destruction of Alderaan.
Upon injuring Kylo Ren during their duel, she becomes convinced that her heritage is the thing that is causing her to continually give into the dark side — since this is the first time she had given into the dark side after she learned the truth of her heritage. Because of this, she exiles herself, convinced she is meant to end up just like her grandfather, still held back by her belief that no one is going to give her approval if she were to become a Sith.
Luke Skywalker, aware of her heritage, shows up to her and dismisses what she believes, explaining to her that her value is determined by her heart and not her heritage — proven to be true by Leia deciding to train her, despite how she has acknowledged who Rey truly was — and that said heritage does not define who she is and how her future is going to turn out, urging her to face her fear, confront Palpatine and save the galaxy; this convinces her that she is able to do the right thing, regardless of her heritage.
Right at this point is the first time Rey truly acknowledges the existence of her core belief of self-worthlessness and how it has been holding her back her entire life — when Luke informed her that, “Confronting fear is the destiny of a Jedi,” she applied this to her fear, that being her feelings of self-worthlessness.
Of course, she goes to confront Palpatine on Exegol; he urges her to perform the Sith ritual; she must kill him, and by doing so this would allow his spirit to possess her body — she would become the Empress of the Sith. At first she refuses, but Palpatine warns her that the Resistance is in danger of annihilation by his forces, convincing her that, by becoming the Empress of the Sith, only she can prevent this from happening.
Convinced that the Resistance is going to be giving her validation for as long as she exists, ruling as the Empress of the Sith, she accepts his request — representing herself giving into her core belief of self-worthlessness as well as her lie that only others determine her value; Ben Solo, however, returns for her — proving to her that she is valuable, regardless of whether she becomes the Empress of the Sith or not; this allows her to refuse the ritual and stand aside Ben against Palpatine.
Palpatine, however, drains them of most of their life force to rejuvenate and strengthen himself, afterwards literally throwing Ben Solo into the chasm — Rey is left weakened and alone.
Feeling unable to defeat Palpatine on her own, she turns to the Jedi of the past for support; in response, they encourage her to try her best to defeat Palpatine, regardless of how puny she is in comparison to him — now, she has enough strength to not only refuse the lie she had believed her entire life, that she is worthless, that she is only worth something if other people think she is, but also rise and stand against Palpatine.
He dismisses her as nothing, no match for the “power in [him];” instead of succumbing to his remarks, she ignores them and responds back with her own, self-made sense of self-worth and self-esteem… that “she… is all the Jedi,” and the icing on the cake is that she has pulled in the Skywalker lightsaber, the weapon she has felt unworthy of using for so long — she finally feels worthy.
No longer held back by her irrational, toxic core belief that she is worthless, having come to terms with the truth that worth and acceptance comes from within and not from other people, Rey destroys Palpatine — the embodiment of this belief — once and for all.