I read the book I’m looking for as a young teen or pre-teen. 15-20 years ago. I believe it was YA because it was in my school library but the subject matter was more adult. There was a girl in her teens, attending a pre-college program or a school program of some kind but I believe it took place at a college. There was an undercover officer in it posing as a student and became close/friends with the main character. There was some kind of drug ring happening at the school that was being investigated. The cover of the book or back cover of the book had a window on it I think?