oh you know, my best friend who is also my brother in law is a smoker, and we didn't bother sugar coating, we made it blunt. "You can't hold her until you quit smoking" . That was it. Of course he was annoyed, but he knows deep down that it's perfectly reasonable, and now he is content to simply look and not touch.
Just say what you have to say and be done with it. Like I said, it's a perfectly reasonable request and she will understand that, even if she is a bit miffed!