Thanks for your replies everyone.

It's nice to hear that you think we're on the right track but I'm still not too sure what we are going to do in this particular instance...given that she is waiting for her punishment to be handed down... and has been particularly sulky & horrid today not helping her case, is she?
Just wanted to give you a big Jasp. Like the others have said I think you are doing a great job, the most important thing you can do is keep the lines of communication open. I have to admit this does bring back memories of my teenage years. Based upon the way I behave as a teenager I tend to think that you are best not to punish her. I think if she gets punished that is going to make her want to hide these things from you in the future and that is the last thing you want. At least if she is able to share with you and feel that she can talk to you about what she is up to you have opportunity to guide her and encourage responsible behaviour. But if she decides to close up and keep things from you for fear of getting in trouble and being punished you're less likely to get the opportunity to guide and advise her.

Anyway, just thought I would share my take on things, I was a horror teenager who started smoking and drinking around her age. My mum would do everything to stop it, which just made me rebel even more. In the end I got shipped off to live with my Dad who had a totally different approach. He never said 'no' to me, just advised me and gave me the freedom to be a teenager and do what teenagers do. In my case it worked, being given responsibility not being told actually meant that I settled down. For him it did mean sleepless nights, but he knew that if things got out of hand I would call him for help rather than try and sort it out myself for fear of getting into trouble.

Good luck with it hon xoxox