I feel for you too. Nonetheless, it's a wonderful thing that she feels comfortable to talk to you about it. I wouldn't even assume that she hasn't already been active.
Tell her clearly what you think is right; be her parent not her friend. This includes making sure she continues to be comfortable talking with you, even when she goes against your wishes.
I have a great relationship with my D17. Last year, she came to me (and w) and asked for birth control. Even with our strong level of communication, it was very hard for her. She eventually explained that she had already been active with her BF of a year. Of course, it shook me up! We had already had all the detailed conversations outlined in the suggestions already given you. We also had limited her opportunities to be alone with the boy. SO, she resorted to lies inorder to have a chance to "consummate her love". She called it the "greatest day of her life". sigh. We were understanding, but gave her some pretty strong consequences.
Now, a year later she told me that she regrets how she had her "first time", and that she was too young to make that decision.
My suggestions to you: Prepare and inform her the best you can, Be a Parent and set boundaries and examples, Be prepared for her to make these big mistakes, Keep the lines of communication open.
M:42|W:40|D:17|S:13|Bomb:10/23/09 Awoken's Current Thread