"Talk to her as a peer, a friend, an acquaintance; anything but her mother".
In my opinion that is the last thing a parent should do. Parents are not peers or "friends", you are a parent, mentor, teacher, judge and jury. In the military they say "Familiarity breeds comtempt" and I believe it. You want to be a friend and then you may have to take her phone away or ground and then it is a whole new ballgame. Now you have betrayed her and she thought you were friends etc.
Oh god what I am about to say is extremely painful ;) Gypsy is right, you either got it right already or it's probably to late.