At all time it is following her, walking towards her, unless she manages to pass it along to the next person.
I'm sure you have and will give her all the do's and don't as you sound like you have that kind of relationship.
I have always told her that when shes ready to let me know and we can sort out contraception etc, but now shes told me its freaked me out a bit as i didnt expect it so soon I really dont know how to deal with it as if i say no she will probably do it anyway but without my support, but if i say yes its like saying yeah go ahead its fine please advise Legally, if she has sex with her bf, he can be arrested for statutory rape as you DD is under 16.