Yeah but there's also JC to consider.
I wouldn't assume that out of hand, people can be extremely irrational when something emotional (like the death of a parent, and their own death) is involved. I once had the pleasure of knowing a guy that was certain he was under siege by spirits/demons because his dog was sometimes restless, and his dryer would thump and vibrate. Granted, he also did meth for several years and had other problems besides, but still. Take the craziest thing you think a person can ever do or think, and there will be some guy somewhere that did something crazier for an even worse reason. There's always that one guy.
It's likely, but not certain, that she just wanted to shut him up about quitting smoking. Most smokers know the negative health effects.
I'll bet it worked too.
"I might die if I quit smoking!"
"Oooook...<walks away>"
You're right though I can't presume to know if that's what is going on in her head as I can't read people's minds I haven't even talked to. That's just the most likely scenario given most smokers do know it's bad for them.
Conversations with smokers often go like this:
"You should quit smoking it's bad for you. It can lead to cancer, cardiovascular disease, emphysema..."
"I know I should. I've tried to but I can't seem to quit."
Now why do you suppose a person can't just decide to quit? Because their conscious mind is not in control of that behavior. Their subconscious is. By default, people are not even aware of their subconscious let alone what it's doing, why, or how to change it.
How many times did you blink in the last minute? You have no idea because that is a subconscious process that "runs in the background". Only now did you become aware of it. Sure you always knew you blinked, but you don't have to think about it, it just happens automatically. You're not usually consciously aware of it.
Most people would be utterly surprised at how many subconscious processes are running in their mind at any given time. I can list some if you're interested.
Negative behaviors are often subconscious because if they were conscious you could just decide to stop doing them, they would be fully within your control. You wouldn't be telling people "I try to but I just can't".