[ImpactBreaker]

The fact ayu is healthy is not a proof she doesn't smoke. We all know most of the diseases caused by smoking are chronic, after the person has smoked for over 30 year +. Many smokers manage to keep "healthy" and have a healthy appearance for years even if they smoke a lot, and maybe that's one of the reasons they won't think about quitting, because they won't be really be bothered about the consequences since they only appear late.
Some singers smoke and manage to keep their vocals fine. Again, not a proof.

There's no real proof whether she smokes or not. None of the speculations are solid enough. The pictures available are all blurry and unclear. The most reliable fact I'd mention is that most likely ayu isn't a heavy smoker (if she's a smoker). If she smoked heavily, we'd have already seem much more evidences than just those questionable ones.