The student council president is totally Kaguhara's big sister. That double ahoge + their likeness.
The girls in that storeroom failed to see how degenerate Kaguhara truly was, just like the scp mistook her for one of the 'pure' student, just because she superficially adhere's to the formal school uniform.
Here, most likely because she knows that Kaguhara dutifully follows their insane neatfreak home routine too, while keeping private her filthy mind.
Now, I wouldn't be surprised if Kaguhara is far gone enough to lewd her own sister. The strict student council president? Common and powerful trope, like for Mari Kurihara in Prison School for example.
It must be done! To fight back against fascism by destroying her too-rigid core values, of course.