Uh-oh! That's no bueno :/
This really depend on your ages. If you are on the younger end (13 and below), I would maybe consider telling her parents. And I'm not quite exactly sure what kind of "books" these are, but if they are what I think they are, kids that age (or any at all (guilty)) should be consuming that content, and she needs to have a talk with her parents.
However, if ya'll are older or going to an adult is not an option, I would just talk one-on-one with her about your concerns. Your worried about her mental and emotional well-being! Ask her if she feels wrong reading/ seeing these things. Just tell her you think it's wrong, feel free to voice your concerns!
But, in the end, it is up to her the choices she makes. But good on you for being a good friend and having morale.
Good luck, I hope this helped a bit. Feel free to lmk how it goes!
:)
