Where does Ginny hide the advanced potions making book?

Answer 1

He hides it in the room of requirement where there is a load of other stuff that's been hidden there by other students. In this room, Harry first glimpses the Lost Diadem of Ravenclaw, which he later recognizes as a horcrux.

Answer 2

She hides it some where inside of the room of Requrment (not sure how spell) It is the same room they where using in the fifth book/movie as an area to train as the DA (Dumbledore's Army).

Hope this has helped you. :D