Friends

So my two best friends are both younger then me, one is 12 the other 16. I love these to kids as if they were my sisters, which is why when the 16 year old starts making the exact same mistakes I did I get scared. The choices I made when I was that age led me down a very bad path, and I warn her, but of course being 16 and naive she says its different. I don't see the difference between us, but she does. I am so afraid of her getting hurt and I just don't know what to do. I know I have to let her make mistakes and grow from them, but she is naive. She doesn't understand the world because she has been sheltered from it her whole life and now because of a divorce she is being thrown into reality with anyone to guide her. How do I tell her that she needs to be careful.....