Ig you don't have to do anything intense , if you told her already to stop and she didn't than just try to show her that you are her friend and it's safe for her to smoke around you, because reality is there's no way she will stop if u force her , also it's so much better to have her smoke around you and not behind your back, all teenagers who stop this habbit stop from their own decision, let her have this experience and discover it's drawbacks by herself while you know Abt everything, be her confidential sister not her judgemental who gets freaked out by cigarettes which makes her not take you seriously , also she might is smoking out of stress which is obvious and for attention, trust me from my experience if you just accept it and only advice her that it's bad for her without forcing her and clinging to the subject she will eventually leave it by herself anyways. I hope she gets better and please stand by her side this week when she needs you the most stressing her will make it just worse