My 21 year old sister smokes. How do I convince her to stop?

I love her soo so much, and I know she can't help it cuz she's addicted... but a long time ago when she was like 14 one of her friends offered her a cigarette and she was dumb enough to take it [I'm not going to get into details, other stuff was going on around her... she was kinda stressed...] and so now she smokes. Her fiance also is a heavy smoker... I really want their kids to be healthy and I want my sister to be healthy but she smokes!! WHAT DO I DO!?!?!?!? please help!!My 21 year old sister smokes. How do I convince her to stop?
Have her talk to someone who has emphysema.
You can't. She has to do that. Nobody will ever be able to convince her unless she truly wants to do it herself. Unfortunately, that's how addictions work.
However, you should still voice your opinion about it to her, just don't be annoying about it, and try not to lecture her.
If she knows that it concerns you, then at least she may THINK about quitting. After that, there's not much you can do.
U should explain to her that it can give her troat cancer or cancer to scare her. show her pics of wat happens to people wen smoke to much
tell her how much it costs in the long run. like add up the price of how many packs they buy in a year. and then show it to them. make sure you add tax and things. and the numbers are scary. like 3,000 a year on cigaretts. they could be spending it on more important things.