I think I kinda-sorta get it now, in a rather weird way.
In her mind, his smirk was a betrayal; the worst one in fact: she essentially endured the bullying for him, but when he smitked when she was at her lowest, she felt like he was making fun at her. Everything she endured meant nothing for him, or so she thought. That's why she says now if he came to her as an idol to laugh at her, because, in her mind, he did the same before.
That doesn't excuse nor explain the torture; but I've got this weird impression that she was trying to make him grow a pair. I always thought that many of the tortures worked because he's too much of a coward to call her out on them (stalking notwithstanding).
But it's my opinion, it doesn't justify what she did AT ALL and it's not like anyone here is giving her a chance (she doesn't deserve it, to be honest).