take it easy and have some nerves. It is good thing that you and your wife have found about it. But must say that you should already have told some stuff to your daughter about behavior on internet.
Please be aware that your daughter is very grown respecting her possibilities in using computers, kids are just too fast these days. And they doing it like they are not at all innocent so they need education very early about it.
So please think on education plan for yourself and your little angel. Children today are so capable of using tech things and we older ones have to learn them very early; it is sad thing that parents regularly don't see those risks on time. So we adults need to learn them how to use it safely and what are risks there in first place. Those are things that we learn kids many years ago for their real life, there is same need here too, they would not lost innocence because of that. Consider it like showing her how to go across the street alone.
So please consider to put some rules in using internet, like this:
let your daughter know that you are interested in her online activities;
Place the computer in the living-room - this is must;
Set some rules for using the Internet (when is allowed to used it, at which hour, is it allowed to have Facebook profile, is it allowed for her to go to chat rooms, is it allowed to use camera, please put also some filter for pornography etc.)
Explain to her who is a stranger in real and who in virtual world;
Explain to her what are potential hazards of meeting the person that she knows only through chat and online;
Explain to her the dangers of sending own pictures online, as well as the concept of child pornography- yes she can understand that easily;
Alert her that conversation with strangers especially on sexual issues can be dangerous for her;
Explain to her that sexual activity between adults and minors is punishable offense;
Martin, it is important to remember:
your kid may know more about technology than you, but you know more about life. You are allowed to set rules and request their compliance.
That is the most basic role of parent and you are very good parent...
I'm sure that you'll be good in all this