Girlfriend (25F) has started smoking at work, and it's a complete turn off for me (27 M)

Am I being reasonable for considering break up because my girlfriend has started smoking?

A bit of context, I (27M) started dating the gf (25F) over a year ago. She did not smoke back then, and I wouldn't want to date a smoker in general since I feel like it's pretty disgusting and self-destructive. However, in recent months, she started a new job that is a bit more stressful, and has started taking smoking break with colleagues. I told that I do not like this at all. She should be mindful of her health, and this is a slippery slope towards a lifetime of addiction and health consequences. It seems really stupid to even start. She told me that I don't understand her and that smoking breaks really help with her job (waitress). I argued that just for a momentarily relief for her job/money, she's setting herself for a much bigger issue. She doesn't buy this argument.

Honestly, while I like her very much, it has been a complete turnoff in this aspect. I understand that it is her life and her choices. She can do what she wants, and I should not be controlling.

In the end, I mentioned to her that, it's pretty much a deal breaker -  I will not date a smoker, she can do with whatever she wants with this information. Obviously she is pretty upset. Not sure if I'm being too harsh and whether I am being reasonable?