Grammatically, there is nothing wrong with them. However, the sentence "I haven't been in good health since I smoked" strikes me as strange. This sentence means you used to be in good health, back when you used to smoke, but you're not in good health now that you've quit smoking. A more logical sentence would be "I haven't been in good health since I started smoking".

Both sentences are fine and easily understood. Whether this is your intent, we cannot tell since there is not enough context.

They're both rather awkwardly expressed. It's not clear what you're trying to say. Do you mean the following? 1. She hasn't been in good health since she stopped working at that company. 2. I haven't been in good health since I started smoking.

Here "since" is used in temporal sense.