I agree that delving into the psychology of sex and suicide (especially suicide) is probably not a good idea. In my experience, reading a matter-of-fact record of adult experiences (such as war, sexuality, or mental health) differed significantly from reading material delving into the psychological experience of an adult experience. I was quite interested in war as a kid and read a lot of history books, The Iliad... It was an entirely new game when I read All Quiet on the Western Front, which chronicles not only the more-factual side of war but exegetes the psychology of a soldier's experience, and it was more than I could deal with as a young teen.
Since she likes horror, scifi, and fiction with conflicts, she might like The Jungle (mostly pg/pg13 subject in there), something by Jules Verne (lots of good novels with less mature content), a Russian novel (In the First Circle is a pretty appropriate book about spiritual and politic conflict in characters, as well as some of the implications of communism), or perhaps a longer Poe story/collection of stories (his tales of deduction and of imagination are based in rationality rather than in psychology with respect to the horror).
