A wise person once pointed out to me that if someone was lying to me, I should look at what I had been doing to encourage them to lie. You seem pretty hurt that she was hiding this from you, but you had effectively punished her before for telling you about smoking, so her hiding it from you was at the very least perfectly normal human behavior.
Now, for the rest of this, bear in mind that I watched my father die from smoking-related heart disease, and watched a boyfriend’s grandfather die from emphysema. I have not quit smoking, but I did quit caffeine.
And after I swore I would never even date another smoker (first lover was), I ended up married to someone who smokes.
I think you’ve already thought about this, but the first thing you need to do is to decide whether it is more important for you to have a partner that doesn’t smoke, or to have the love of this person. If you decide that this person’s love is more important, you do need to accept that she may smoke the rest of her life and she may die of smoking related diseases. (Of course, we will ALL die. She might die tomorrow from something completely random).
Your next step is to apologize for trying to control her behavior, and to let her know that you love her even though she is still smoking. Let her know that you accept her, as she is, weaknesses and all,, even though you still don’t like the smoking. If you can’t accept her as she is, go back to step one.
You may need to repeat this mantra: “When she smokes, she still loves me. When she smokes, I still love her”
Next you need to set boundaries. Just because you are accepting her smoking in general, doesn’t mean that you can’t ask her to do certain things that affect you specifically. You can ask that she not smoke inside your residence, and that she not smoke around you because it makes you sad. (If her smoking makes you angry, … am I starting to sound like a broken record?)
After you have done this, if you mention her smoking again, it should only be to tell her that it makes you sad, that you will help her in any way that she asks IF she wants to stop. And you should only do this if you can do it with love and acceptance, and hopefully, a certain amount of humor. If you feel anger or, worse, contempt, keep your mouth shut.