There are some posters who seem to be making an assumption that the visiting girl was intentionally going to that site and is a guilty party. (At least that's how some posts look to me). And that she is not well supervised on the computer.
There is no proof of either.
All that is known is that
someone went to that site. Maybe her, maybe someone else.
WHO it was or whether it was accidental or on purpose is not known.
It could have been anyone who had access to that computer and there could be other reasons besides that someone intended to go there. I know I have been sitting with my DDs when they accidentally got to some of those types of sites, so I know it can happen innocently.
For example, this link says it goes to the
Disboards Theme Park Board, but does it? (Don't worry, it doesn't go anywhere bad).
Could they have gone to an innocent looking link from the site they were on right before that? That has happened to me and to my DDs, so I know it can happen. That is how some of the "bad guys" on the internet work, by tricking people to get to their site. I even know someone whose business site got hit by internet vandals and his links that were supposed to go to more information about his products, linked to some pretty explicit sites until he was notified and fixed it.
Could someone else have gone to that site previously and they just typed in the first few letters (and then the computer completed the site as a choice)? If that happened, they may have gotten there innocently and there might be a problem with someone else. (if the OP didn't erase the history, you could probably still get to that site by typing in the first 2 letters).
To accuse that girl of doing something wrong when it might be accidental or it might be someone else is wrong IMHO. IMHO accusing someone of purposely going there is going to make the problem worse if they got there accidentally. They are not likely to tell anyone the next time because this time they got in trouble for something they didn't mean to do.
So, I think the best may be to have a "blameless" talk about it. That you know someone ended up on an explicit site and however it happened, those are not sites that are acceptable to your family. That you know that sometimes getting to those sites can happen to you whether or not you plan to go there. They need to know what to do if it happens and that the adults won't be upset if notified they got there by mistake.
And that if they got there, accidentally or on purpose, they need to know that's not an OK thing to show/take others to.
If they got there accidentally, it may lead to a discussion about the dangers of the internet. If they got there on purpose, they know you are watching.