As one would expect, there are as many answers as there are people and for different reasons. My girls are grown now, and I am glad I don't have to make the decision. I feel you handled it very well, as did your daughter. Also great that you acknowledged that you were proud of her for telling you!
I don't have any advice on what to do, just that you have to make the decision that feels right to you. But, I do want to say that I work at an STD clinic and have had girls as young as 11 with sexually transmitted diseases come to the clinic. I also work as a Nurse Home Visitor for a program that works with first time mums and babes. I currently have two 14 year old clients. Our program has had them as young as 13. Our young ones are having sex younger and younger, yet the part of their brain that can make intelligent decisions about having that type of a relationship doesn't even fully develop until sometime in their early 20's! I don't pretend to have a solution, but do urge parents to be straight forward with their kids about this topic and make sure they are protected!
Good luck and God Bless!