What is the ruling on a wife concealing her smoking from her husband after he has forbidden her from it?

Smoking is forbidden because of the harms it entails. Your wife is sinful for smoking, and you must prohibit her from it, explain its prohibition and harms to her, and prevent her from doing it, as you are responsible for her by virtue of your guardianship. Furthermore, her concealing of smoking is permissible, because when a Muslim is afflicted with a sin, they should not publicize it, but rather conceal it.