Not trying to be a smart ass here TAB but did you ever think of taking her up the road for a tour of Folsom? Sometimes a little shock value is a good thing.
As someone else suggested earlier, none of the armed forces accept anyone without at least a GED, if she isn't willing to work hard enough even for that, no amount of forced anything is going to help.
Sometimes people just can't be helped, or don't want help. Don't give up but don't take it personally!
This discussion gives me reason to give my daughter a great big hug when she comes home, though I don't really need a reason!