I have the same problem with my mother so I know how you feel. She doesnt see the prob with smoking around my kids. My husband smokes as well, but he wouldnt even consider lighting up inside at all. I told my mum we wouldnt take the kids to see her if she didnt stop, and she has got a lot better, although her house stinks so much, we all come out of it smelling like ashtrays!
The worst of it is though, both my kids have breathing problems, my eldest (3) has been diagnosed with asthma. Iv never smoked, and never put my children in smokey environments. My mum on the other hand, smoked her way through her pregnancy with me, smoked all through my child hood, and I dont have any chest problems at all!! It just makes it very hard to make her see.. and she brings this point up every time we visit!!
Sorry I cant be of help though!