I have an instinctive reaction against this, and I'm sure if I ever become a father, I wouldn't like it much, but seeing as I consider most people to become mature enough to make these decisions for themselves around the ages of 16 to 18, my natural desire to protect shouldn't be applied too strongly. Advise caution, and let her know that she should never give in to pressure, but beyond that I must let her go about her own business in peace, even if I don't necessarily like it. The best thing to do is be there if it all goes wrong.