Yeah she's pretty annoying, I also dislike her but like she's a kid and kids are sometimes like that so I'd say it's a pretty accurate portrayal, we often forget about such simple things because we're used to reading about regressors and so we forget that they are older than the rest of the kids around them.
Ik, that's probably the main reason I can tolerate her over other 'female characters' (saying that with marks to emphasis how inaccurate portrayals of women in action manhwas with a male main tend to be) is because she's just a kid - though a tween one that's learning to be better. I think the only unreasonable part is the extent she goes to in her personality and how almost attention seeking she is (on the downish low) despite being a relatively well rounded and well liked by others character. It would have been more logical if she didn't show such level headedness most of the time but loses it when the MC comes in the picture - primarily at the beginning. But I certainly agree with you.
I'm sorry, but Christa really got on my nerves. Not in a "I hate her" or "I wish she wasn't in the story kinda way", but more of wow, she really fkn annoying and they should've toned it down by a metric ton. I felt my energy sapping away everything she opened her mouth - it's just... If she was so talented and so many people supporting her, you'd think she would stop more often to use her fkn head and stop being a dick to certain people and biased towards others. It really does feel like I'm listening to a kid whine and it's not the end of the world, but it's certainly makes it hard to read the story when she tries to take over every panel she's in for no good reason.