Buy her a book. Tell her she can talk to you about this kind of thing. Warn her that there is a lot of unpleasant stuff on the internet which won't help her to understand about physical relationships. And check your restrictions - but if she ended up looking at Wikipedia she probably couldn't get to anything racier!
Oh and make sure you let her know that sex is a positive and enjoyable part of adult life, but that it's best if you don't rush at it but wait till the time is right and you feel you'll be happy to look back on your early experiences fondly rather than with embarrassment.
One day I checked the search history on our computer and it showed "Mario having sex with Peach" !! yet after checking the crap stuff that cam up from this and some hyperventilating (!!) I knew this was the beginning of a healthy natural curiosity towards sex experienced by all children as their body begins changing/or earlier as they become aware it will one day change (he was 11 at time, and his brother, 9). We had educated them many years earlier on how babies made with simple language. After this, I borrowed relevant books for their age group from the library along with others and opened the topic up (to their horror, they were not looking at them!) so, just left them next to their bed. We let them know it's OK to be curious but that the internet had some inappropriate, ugly info/pictures not representing loving relationships etc, and it was not OK to learn from there.
This is the first time I have ever used mums net. I am a mother of 3 mostly wonderful children. My oldest is a girl of 11. This morning I did a quick search on her computer history ( we have a shared family computer, she has her own log-on with restricted access) and found that she has been trawling wikipedia for anything to do with sex. I'm not sure how to talk to her about it, she is pretty embarrassed, I don't want to make things worse. Any ideas?