In a flashback, Taystee and Poussey meet for the first time in the library on Taystee's second day while Poussey is working in the library, but in the first season, Poussey is learning how to shelves books from Taystee, who clearly runs the library. In fact, in season 1 episode 8, Poussey thanks Taystee for showing her the ropes and getting her assigned to the library and she only takes over running the library after Taystee gets paroled.