I think I can offer some insight here...
I'm a converted cigarette smoker myself, 3 years this November. You have to want to quit cigarettes, in order to quit. And even with cigars, you still have to kick the cigarette habit - the quick smoke after a meal, or when you're stressed, or bored, etc... Any way you spin it, it's a big change - more on that later.
I haven't cheated since the day I quit, and cigars definitely allowed me to stick with it - one of the big challenges for me was that I would chain smoke when I drank, and I like a beer or 2 on most nights. I abstained from alcohol for a short while after quitting, but I like beer, so I wasn't giving up drinking - that's too much change at once. So having a cigar with my Nattys kept me from going weak and running back to the Camels. One could argue that my love of cigars is just replacing one crutch with another, but that's beside the point.
Point is, cigars CAN help kick the cigarettes - but you (or in this case, your girlfriends) still have to want to quit cigarettes, and that's it's own thing. It's a major change, so take it slow by smoking both cigars and cigarettes for a while. Quitting cigarettes is one thing, learning to love cigars is another - don't do them both at the same time.
@broadleaf - if she likes the American Spirits, you might be able to incorporate cigars into that journey...? I still suggest slow and steady overall, though.
@Gmab980 - yours might be a tougher case to crack... maybe pick up something light with a sweet tip, like Fontanas or Isla del Sols?