Well, I would say that grounding you isn't the way to teach you the lesson she wants you to learn, which is that smoking is bad for you... what it seems to be teaching you instead is that she's acting in a hypocritical way.
However, my guess is that she wishes she could quit, and she's overreacting because she: 1) feels really bad that she isn't a good role model for you about smoking; 2) feels somewhat responsible for your experiment with smoking; 3) feels panicked that you may become a smoker; and 4) is at a loss for how to teach you that smoking is bad, because she can't really point to herself, can she?
So what I think you should do is go to her, and reassure her that you won't become a smoker (you won't, will you? Because it really is terrible for you, and since you are not addicted and really have a choice in front of you about which way to go, here's your opportunity to make a good choice for yourself).
(continued next message)