The only reason Marie didnt take down the false news was so that she wouldn't get kicked out of the club and that club is her only ticket to convincing her dad to let her move into a dorm. It's sad that her brother tries to keep Marie from moving only because he doesnt want to take care of his dad and the housework even though he's way older than her. Honestly that whole family seems to be blind from the brother's acts that's probably why marie has no one to talk to about this
Think of it like this if you were her and you saw haejoon in that situation you'd probably think he was the bully too, She doesn't personally know Haejoon so she can't really sympathize with his situation, she's only thinking about how bad her situation is because she doesn't really know what's going on with Haejoon, probably if she personally saw Haejoon getting treated like trash she'll change her mind about the whole news thing
She doesnt seem like the type of person to let someone suffer so much, remember she posted the news not only to get a big story but to also help the victim in a way, sadly it didnt turn out so good. I'm not saying what she's doing to Haejoon is awful but you gotta think about her perspective on this, all the characters in this webtoon are great characters
You guys gotta realize that Marie had to do all the housework at such a young age due to her mother leaving, apparently she also had to deal with an abusive brother, I'm surprised she didnt turn out to be a bully