Kutabarie, I'm making a massive assumption here, but have you ever been bullied? That comment makes it look like you haven't...
For a lot of people, it's something they can't fathom escaping, like a 'hole they are trapped in', so it can be hard to try and change that.
Saying she should just 'try and change it herself' is just like telling a homeless person to just buy a house; neither is helpful, neither is a clever way to go about suggesting a solution.
Of course, that doesn't mean I agree with her actions. Well, I can see where she's coming from (I mean, we all did), so I can understand why she keeps behaving this way.
Because she has manipulated MC, she is able to exact revenge on who she wants, all without consequences, all without getting caught. It's perfect for her, really. All she has to do is pick the next target.
She won't stop unless he says no, but he won't, so it's a stalemate. Something has to change for her to change. It has to be one of the two, and at this point in the story, it's unclear who will, or if anything ever will.