There are very few times when it is ok to bring in the big guns and scare the crap out of a kid. This is one of them.
****THIS DOES NOT APPLY IF SHE MAY HAVE BEEN SEXUALLY ABUSED****
Do everything you can to find out why she made this video, check into every possibility that she was abused. If you can be completely confident that she was not abused and this was just a dumb kid thing, SERIOUSLY talk to her about the penalties for an underage kid making a video like this. Talk about arrests, talk about jail, talk about being on the sexual offenders list. She isn't too young to understand, but definitely explain to her WHY these things are in place, that there are bad people out there in the world.
Remove her unsupervised computer access. Limit her time even supervised. Find a class being given by local police about this type of thing and attend it with her (and make SURE she knows not to say anything about her activities at the class; do not put her at legal risk.) Find out which friends she's been with that have made her think this was ok and cut her off from them.
It sounds totally harsh but it's her life riding on the line; if she gets caught with something like this, she could ruin her future.