My Inlaws live right next door ... she has been a chain smoker for decades - the house absolutely STINKS and we can't have any windows open on that side of the house purely for the putridness that wafts through. She has been told she will go blind and needs and operation and to give up the ciggies - but in her mind - it's easier for her to go blind than give up the ciggies.
It was made quite clear by her son that there would be absolutely no smoking in our house or around our children - so she chooses not to come over. She chooses to bellow over the fence at her son and her grandchild (I'm due in another week with bubs number 2) with the ciggie hanging out of her mouth.
There is no point in asking her to change clothes - the house is so backed up with years of cigarette smoke that it's just engrained in everything.
I guess I'm lucky that none of my friends or other relatives smoke so haven't had to deal with it but I have held other people's babies whos parents are smokers and can't help but gag.