I don't think they can tell, only if she forgot to take a fresh mint and the MW got too close to her breath!!! She shouldn't smoke, but I also know it's hard to give up. Story - a friend of mine smoked, she found out she was pregnant and she quit. But she found it hard. She didn't want a cigarette but found she was stressing when she wanted one. Her solution was to light peoples cigs (this was only when she was out, she kept no cigs in the house!!), she would light one and pass it back. Now this is not good either, but it was better than her having a whole one. Fortunately, she was ok, although her daughter did have to spend a night in an incubator as she was a little early, but no ill effects thank goodness. If she can't quit for her and her baby, maybe you could suggest that. Then from there she may be able to quit easier. Just a suggestion.
My OH smokes and I have now found that I can't stand it, probably knowing that it's not healthy but also cause my sense of smell is like the Bionic woman would have!!! It always seems to drift in my direction too. I have asthma but not bad, not really used my inhaler in over 2 years since moving here (clean air!). I have found over the last week or so that I am a little weezy, not bad, but worries me a little. Gonna ask the doc today whether I can still use my inhaler if needed.