Yeah, I don't get it either.
She's not exactly the most likable character with her annoying tsundere personality but...nobody in the comments actually says WHY they hate her so much.
Almost makes me wonder if the hate is due to ch 87's fighting cock-block she did. Because so far THAT and her tsundere personality are the only reasons to dislike her, but not hate as some people do.
But speculations aside..
I too wish people would mention why they hate her or at the very least if the reason is ages in the future/the novel. Because that shit can be commented when the time comes, no??
Otherwise it's just confusing (and annoying, tbh) to read all these future-happenings comments all the time whenever there's an update instead of comments ABOUT the update.
And I'm not even talking about spoilers. Just the legit confusion that arises when people talk about stuff that has nothing to do (yet) with the webtoon we are reading here...
The spoilers defo play a big role.
I think another reason would be her tsundere personality and cock block like you said.
If I look at it from a personal perspective because I've also felt that way in the past about any female lead in such manga, but now it's died down thankfully;; I'd say people who dislike her feel a bit jealous and that the girl "sabotages" the guy somehow (Although it'd be a bit boring without the spice).
Personally I both like her and dislike her. She's strong even though she was a bit annoying in the past I acknowledged her and that she cared for Art, especially when they were kids and Art had bursts of pains, and at his sister's birthday! She's graceful and all, but she also reminds me of those mainstream female leads.. you know? She's a bit too perfect. At least Arthur's story was a bit more realistic.
A lot of people (including me a bit) have got a problem with females in such manga, usually because of their patheticness. Pathetic once, pathetic always they say ! But that's not necessarily true. I liked all girls in this manga.. Except for the King's daughter coUgh, I don't know why!
And anyway, despite all that, they are teens! You can't expect them not to have their horny/romance moments either! Okay, they're super powerful and they sounded and looked like they were 17 when they were 8 but damn..(⊙…⊙ )

If y'all may enlighten me why y'all guys hate the elf girl because I don't get it .