I don't think permission should be required, but it's fine to put it in the teen section if the book belongs there.
I was just thinking about "Forever" and I couldn't remember who wrote it but I read it at about that age (middle school). And I always knew plenty of girls who read the bodice ripper romance books along with their moms. My mom and I were never into those books but I was allowed to read whatever I wanted from the library, we often went to a local library several times a week and we were always encouraged to read whatever we wished.