I was 14 when I first had sex and if given the opportunity would have at a younger age. Some people are just ready for that sooner than others. What's done is done. I know its super shocking to you and your instinct is to protect her but just be supportive, have the safe sex talk and all that jazz. You may think you're a bad influence but you obviously care about her. Regardless of your own choices, you can still guide her. She might even learn from mistakes you've made. You might feel she doesn't need you now, but she will. Be her rock, she'll appreciate it down the road.