How to deal with a family member?

hey im 20 (female) and i have a little sister 16 gong on 21 we always used to argue because i didnt agree on her lifestyle as she was too young for the things she was doing. she sat down and wrote me a letter one day and when i read it it made me sit back and think. maybe i was being a little harsh... i dont know if it will definately work but maybe you should give it a go?? write your sister a letter and tell her how your feeling and also try to understand how she must feel too. think if my sister had tryed to sit me down and explain all she had wrote in the letter we wouldnt of lasted 10 seconds but with a letter i couldnt get away from it and couldnt answer back to it. i was able to sit and rea her point of veiw. good luck :)