She isn't pushing against barriers because you've become her 'friend'. They push against barriers all through their childhood and teen years, just to make sure that the barriers are there. And that's the important bit. You set the rules, you make sure they know the reasons for the rules, but you enforce them, because then they know where they are, and that is their security. If they can rely on you to stop them pushing past the barriers, they'll feel safe. A child (or teenager) who finds the barriers moving away when he or she pushes is not a happy child.
As far as getting her to do as she's told (not that I'm a good one to advise on this! I can't get my 9 year old to do as she's told!) by teen years (How old is she by the way?) you have to start keeping the telling for the important things. The only way I've found then to enforce it, is the old removal of privileges. "If you don't do this, then you won't be allowed this". It's reasonable, logical and appeals to their sense of justice, even if they kick up about it like mad!
And the other thing i believe is talk to them, talk to them, talk to them, all the time. Explain what you feel, what you think and why and allow them to do the same. You may be a parent but they also have to see you as a human being! Good luck!