Marie is really doing some mental gymnastics to try to justify why she wouldn't tell the truth. She's the one that put herself in this situation. The victim told her not to publish the story. The club advisor told her not to publish the story. She did it anyway. And now she knows she can't take it back without getting the club in trouble. She even admits that she isn't that invested in the club or school. She's using the club as a way to justify to her father why she should be allowed to go live in the dorms.
I'm guessing Marie, like the rest of the characters, has issues at home. My guess is that she's tired of having to take care of her father and brother. That phone call with the grandma really makes it seem that Marie was expected to fill the void that her mother left behind. I can sympathize, but Marie is still destroying someone's life. This kind of accusation can get someone kicked out of school. Do the right thing, Marie!
Also, so cute that Eunyung is getting protective of Haejoon.