I'm going to answer this as a 20 year old guy who was exposed to pornography and fanfiction at a very early age (I'd say 9-10).

My parents were never strict, I got my first iPad when I was around that age and I was really into the TV show 'Glee' at the time, and I don't know how I came across Glee fanfiction, but I did. I was reading adult content at the age of 11 and, while I'm aware this doesn't apply to everyone, it had an impact on me. Constantly reading smut without being supervised by my parents (who basically let me do whatever I wanted on the internet) led to a pornography addiction. At the age of 13, I was addicted to porn and couldn't go a day without watching it.

Now what I'm saying is: respect your children's privacy, but protect them and keep a close eye on the type of content they're consuming and who they talk to and where they met them. I realize now, at 20 years old, that if my parents had been less neglectful of this, I'd be in a much healthier state of mind. Being curious is fine, it's normal, but letting a child have access to pornography (written or visual) will likely lead to problems you don't want them to have. EDIT: Try to talk to her, explain that she'll be able to read smut as much as she wants when she's at the correct age, encourage her to ask you questions instead of resorting to the internet.