I’ve been changing my mind on her, I was pretty annoyed by her then I felt sorry for her cuz she’s still really young or whatever but then I thought about it more and it really doesn’t excuse her immaturity. To add on, when the guy told her the MC was sensitive to magic and could possibly DIE, literally minutes after, the first thing she did when he started feeling sick was use magic on him :|
Oh absolutely! This post only means to dive into the explanation behind her actions, not attempt to excuse them. Being sheltered isn't an excuse for being insensitive or idiotic to the degree that you could get someone killed. She doesn't need to have the maturity of an adult, but a 16 y.o does need to have common sense, which she lacks, and not be spoon fed everything. Her blowing up at the MC was 100% her fault and she needs to own up to that. I'm just hoping they won't villainize her and actually give her a character arc, because let's be honest, with a cast of characters in their 20s and 30s, no one wants to read about a teen villain unironically, or a teenager constantly getting ragged on.

(Mind this is just going off of the chapters we've gotten thus far - 12 - & not the novel)
She seems to be a highly sheltered naïve kid who just reeks of privilege. Here's the thing, I don't think declaring that you will change the world is a naïve/ignorant statement because that's simply not my philosophy, but you can't save the world if you know next to nothing about it and take everything about it on a very surface level value. I don't think I was as oblivious as this one is when I was 16, and her situation is even more outrageously sus because she was legitimately kidnapped and taken into another world and given a burden that had nothing to do with her. It wasn't even a moral responsibility, no they took a child from another world and are now forcing this child to solve their problems.
Now it's not that bad declaring that you want to help regardless because you can't stand human suffering, but that doesn't mean you should forget to think about what kind of people you're among, and what possible lengths they could go to save their own hides, y'know, aside from kidnapping a child. As far as I can tell, she's treating the entire experience as a fantastical adventure because she hasn't stopped to even think about the very real threats her environment poses her. When she yelled at the MC and accused him of trying to make the people who'd escorted her thus far to be liars, her mentality of 'they said nice things to me ergo they're nice' or 'they told me what I wanted to hear ergo they're on my side'. The MC raising the very real warning about trusting strangers was something she didn't want as a part of her narrative.
Additionally, what teen wouldn't like to hear someone tell them that they're saviours of the world or something and basically get an overinflated sense of importance? I bet that's also what's happened to her. She was summoned to another world, made Jesus or something and led away by handsome men to be spoiled rotten. She's just seen the good, sheltered and privileged rosiness of this world and none of its thorns.
Regarding her constantly using the term 'corporate slave' as a way to demean the MC without realising its true implications is such a shitty teen thing to do. It's a thing where you either learn a phrase or something off of the internet and use it in real life without knowing anything about it from its origins to the context to even the meaning, or just use vulgar, cruel language to make yourself seem 'cool' or 'unique' or 'edgy' with all the privilege accompanying this kind of behaviour (eg. teens making rape jokes). It's just her richness shining through guys.
I wouldn't like her character to become cynical or pessimistic (Gods know we have enough Debbie Downers in the world already), in fact I feel as though we all should strive to be optimists, but it would be nice to see her become more aware of herself and the world around her, and take off her rose-tinted glasses. Looking forward to her development if she will have some.