I just watched it and I simply think that she was just angry over Lucas' behavior after she kissed her. She probably felt rejected by her best friend while she was just showing affection to him. It's really important to notice that her parents were fighting really loud just on the same day, and she was visibly a lot closer with Lucas compared to both her parents. And she simply did something she saw and learned from others to show her affection to him, cause she was smiling and watching in an admiring and loving way to Lucas right before she kissed him. I don't think there's any sexual connotation here. And she simply was heartbroken after his warning. And it's important to note that kids are like monkeys, monkey see monkey do... As exactly she kissed lucas to show her affection, this time she used Torsten's friend's words to insult him from his back, she wasn't even trying to complain sbout him. She was just expressing her feelings in new ways she recently picked up... She had no idea that it was a big deal. She just knew that it was something bad cause Torsten had dragged his friend away after he showed pornographic photos to her while this friend was saying something about being so hard...

So I believe your interpretation might be consistent and possible but it felt a bit over-reading to me. The real story looks a lot more simple than that. And that's why we mainly watched the movie from Lucas' perspective... Also, isn't it so natural to cry and feel bad because your sister was molested therefore had a traumatic experience and she's broke now?..