Where is the library? Brenda has already stolen kelly's panties and now i'm stuck.

it's way later

 it's explained there https://itch.io/t/854874/walkthrough the panty stealing event is mentioned line 285

but i'm pretty sure u need to raise ur progress with ash, the very first time u go into library u have panties and u looking for book the teach asked for

after this and some other things u get the library as a location, i didn't go any further