Fuck her.
If you 2 have only been together for a little over a month and she is already giving you a choice between her and something you have been doing since before you met her, then it really sounds to me like she is just trying to think of some reason to break up with you.
Or to only break up with you for a month or so until you can pass a drug test while she dates some other guy or something.
OR she's just a total control freak.
The second one sounds really bad I know, but I do know some girls like that and these days they're more common than girls who actually are upset with the fact that you smoke.

Sit back and take a ong hard look at your relationship.
He she ever flirted with any guys? Called them hot?
Do you do things for her and she just blows them of like they're nothing?
If yes to any of these, then (excuse the harshness) she's probably just a trifling ass hoe.

I've asked my boyfriend to stop smoking cigs, but that was MONTHS after we started dating, and it wasnt an ultimatum, just asking for him to think about what it wil do for his health in the future.

She probably sees that you really like to smoke (and lets be honest, most of us LOVE it), and is using it against you to be single again.


Sorry if any of this was harsh, Im just giving my opinion.
Hope it helps.

B