@ JTT - When you have walked a mile, or even half, in my shoes, you can judge me.
You make the assumption that I am judging you, StevD. If you are confused and I have no doubt that you are, you've admitted as much, and no doubt these trying times aren't helping, think what that sixteen year old is going through.
You haven't reached the stage where you are doing all sorts of dumb things like she is.
In the final analysis, you are the adult and adults don't always act adult like. We're good at admonishing, at restricting, at disciplining, at ... , but we [adults] are often not all that good at listening, really listening.
I think that when you feel that you've reached the end of your rope, you can probably reach inside and find a few more coils lying about, ready for use.
Of course, I can't know everything about this situation, hence my initial advice. I kinda feel that it's always best to err on the side of kids; not that I'm saying I know you're not doing that.
And I know it sounds trite but time
is really helpful; just hanging in there could do a lot for your daughter.