Should I leave her alone(smoking question)?

Okay, please no rude answers, but I need help. My sister is 18 and pregnant. I am 23 and pregnant with my 2cd. (I'm married, so don't say anything about my age). My sister is smoking 2 packs a day of cigarettes. I will admit, with my daughter that is 3, I smoked 1/2 a pack a day throughout my pregnancy. I hated myself and as soon as I had my c section, I never smoked another one, I felt so guilty because my daughter was so perfect. I didn't deserve her after smoking even one cigarette. My dr. said I was fine though. Well, I am not smoking with this one, and my sister is smoking like a chimney, and won't listen to me or my family. She isn't with the father, and she only had twice, she is NOT a . She swears the condom broke. How should I approach this? I explain to her that I took a huge gamble with Kelsey (my daughter), and it isn't worth the risk. She won't listen to me. Do I just leave it alone, and how much harm is done? My dr. says the more you smoke, the increase in risk goes up the baby. Please help girls. I know I shouldn't throw stones, but I hate myself for smoking with Kelsey, and I don't want my little sister to feel like I felt. I learned from my mistake. Any advice will greatly help.