She is far from mature to have progressed this far into a relationship without understanding why she's doing it. I actually think this is a case of immaturity, she doesn't understand her actions enough to say the three words that sum up everything she's doing, she doesn't understand or worse, is ignoring the emotional toll not understanding those words mean in a relationship where they matter so much.
Lack of knowledge doesn't equal immaturity. I think she felt something for Yeonwoo from the beginning and might have agreed to go out with him to find out what that something was. Not everyone is born emotionally intelligent and those who suffer from trauma often have their ability to understand/process emotions stripped away.
She's not going to be 100% mature because she is still a child, just like Yeonwoo. Some adults aren't even 100% mature despite their experiences. Why expect so much from a child who's trying her best?
Its not about her lack of emotion, but rhe fact she she is mature enough to say i shoul break all my relation if you want to acting like a alpha bitch in heat , being possessive and all they turning all questions on yeonwooa head , she doesn't do this to other characters. Just want her to do this lack of bullshit with a less traumatize person , doesn't even allow him to come to her home then goes to his home unannounce, everyone has a idea of Right and wrong even if you lack emotions
Not entirely sure what you're saying here but it still seems like you're expecting her to be mature about everything even though she's a teenager who is also traumatised. It looks like her trauma started even earlier than Yeonwoo's. At least he had loving parents who took care of him when he was a child and are still there for him. Haesol has no one but her friends.
There's no such thing as right or wrong when it comes to feelings. Feelings happen and disappear whether you want them to or not.
For not saying she likes Yeonwoo ... There's this thing some mature people do. It's called thinking before you answer and taking care not to lie to other people just to make things seem fine. Lying is usually very disrespectful, though most people make it seem like it's nothing.
She clearly likes him but she doesn't seem to know what the feeling is, especially in a romantic sense. It would have been worse if she had told him yes when she wasn't sure if it herself. Some people are naturally not very in touch with their feelings, and there's nothing wrong with that, but I'm sure her past has a lot to do with it too.
I still feel sorry for Yeonwoo, of course. I feel sorry for both of them. But maybe try to hold off on the judgement until you see how she ended up like that in the first place.