Yeah man, a lot of nsfw yuri has this problem. Yes, I’m about to try to defend her, although to be clear she raped her no matter what.
Considering they’re second years she’s presumably been bullied by her for more than a year and she evidently finally snapped. After searching for a weakness she clearly felt this was the only attack vector and she thought revenge would make her finally stop. Obviously we know telling her teachers or other authority figures is what she should have done but she’s only 17 and can’t always be expected to be acting logically.
You can even see that she thinks “this is a just cause” on page 4, though of course it’s not. Either way I don’t give her a pass since she’s apparently smart (or so she says), but I can at least see where she’s coming from