She's going to find MySpace, Facebook, etc. away from your house using someone else's computer, school computers, etc., and just putting on security on your router won't stop her from going to a site with free WiFi and connecting. MySpace, Facebook and all the others are not inherently evil, but evil people sure can be found there...and at malls, schools, hospitals, neighborhoods, etc. You'd be far better off teaching her how to be careful...in all places, real or cyber...rather than trying to keep the world at bay.
If you are determined to keep her away from this stuff through technology, get her a very simple cell phone that does not have internet capability. You also need to make sure her plan does not allow for texting either.
This still leaves friends houses. school, coffee shops, etc.