I'm so sorry tgs3, that must be a pain. Is your GF a non-smoker, or a smoker? That's such a weird response (to me, but I know I'm not representative of the entire population...) and to not even be willing to read about it?
I'm afraid I'd be tempted to "quit vaping" for a little while, then manufacture a cancer scare (I guess you'd need to schedule your yearly checkup and go) and freak out about it for a few weeks while leaving really large stacks of material about vaping handy while continuing to smoke and while saying stuff like, "My doctor wants me to vape, but you probably know more, Honey, so I'm going to keep smoking...."
That's actually a terrible idea, but I think it might be smart to set some limits, honestly. Is vaping more important or the GF? Do you care enough about YOURSELF to just set a limit with her, something like, "I will be leaving the house/your presence any time you bring up the evils of vaping UNTIL you read some research."
I've found that controlling people HATE limits, but they often tend to have abandonment complexes, honestly, it seems to go hand in hand, so you may terrify her for a bit, but she'll come around. And, you are just setting a boundary which is a perfectly healthy thing to do in a relationship. Believe me, I've had to do that before, most often with my MOTHER, but sometimes with the husband (not about vaping, but he was pretty bossy early in our relationship and that was Not Going to Work. I actually kicked him out once until he was willing to go to marriage counseling. You have to value yourself pretty highly to do that and it needs to be a pressing issue (it was) but we both gained skills and it was good in the end. Maybe ask her to go to relationship counseling about it? That might be a nicer FIRST approach....
But, in this way me and the husband have both gotten better about allowing each other to do what we need for ourselves, and that's HEALTHY. It can be a chore getting there, but that's HEALTHY.
Anna