Sorry you're having to deal with this. I did too with MIL. I was very concerned with third hand smoke. We told her we would not visit her if her apartment smelled like smoke, we would not allow her in our car or home if she smelled like smoke, and she was not allowed to smoke in or around our house while staying with us. She followed our rules perfectly because we caught her one time. She got in the car one time smelling like smoke but swore it had been a few hours since she smoked. We didn't care, w kicked her out and left her. She always smoked outside her own apartment and would shower, and change into freshly laundered clothes before coming over or if we were going there. Funny though, DH didn't give a hoot about the third hand smoke, he just didn't like the smell and didn't want DD to think smoking was OK. My philosophy was, if I can smell the smoke then there are still chemicals on you. Also, don't let that person think they can cover up the smell with breath mints, air freshener , or hand sanitizer. None of those things remove the toxins.
SAHM to Coralie, 1/09, Siri 9/10, Ellie Sue 9/12, Baby #4 due May 2014.