I guess culture plays a role in this, I see you're from Italy, from what I know they're not too conservative on topics like these (Dutch myself, for the record).
In my opinion
you are she is overthinking it. Sure, teenagers are emotional, and there's lots of things going on with them. But at 13, you should be perfectly able to put everything happening in such a game into context. There's nothing there that books, movies, life experiences and curiousity have not already brought under her eyes some time before, I bet. And even if it is. Sure, you can try to always make sure that these things are first introduced at the perfect place and time, but I feel kids that age can handle a lot more than what
you seem she seems to be thinking.
Of course that's just my opinion, and I'm quite liberal on this subject.
+1 for having good uncle influence, both in concern and in introducing them to RPG/TES
Edit: misread your post a bit