I wrote all kinds of stuff like that at that age. And also really sexual things complete with diagrams about what I thought stuff looked like. It meant nothing. I was a super curious child who would hear a word and obsess about its meaning for weeks. I would be down at the public library on a daily basis reading things like the anarchist cookbook, or the story of O. And yes, I was 8. I never had any desire to do any of these things, I just wanted to know what they were and I wrote a lot about things like this to let my imagination wander. Now with the internet, kids are so much more sophisticated and can find out so many more things than I could even imagine back then.
I wouldn't be too worried about it and I would just keep a close eye on the both of them for the next few weeks to see any changes in behavior. If all systems are go, no talk should be needed. Unless you are that kind of parent and she is that kind of child. (my mom wasn't and I wasn't...)