Is she truly comfortable with the size and weight of a mod? It might be a size thing that she has issues with. She might do better with a slimmer and lighter eGo?
I happen to believe that finding a couple of flavors of juice that you don't mind using all day to be equally, if not more important, than the battery device. Has she tried a variety of different flavors? Is she hell-bent on finding a flavor that is going to taste like a cigarette? You know the drill for that.
What juice carrying device is she using? She may need to try a variety of types to find the right vape experience for her. If I had started out using clearomizers or a clearotank (Vivi Nova), I'm not sure if I would have been as successful quitting, I just prefer cartos and cartotanks.
Is she resisting vaping with typical coughing issues? Many smokers resist vaping by exagerated coughing and saying, "That's way to harsh for me!" If she is sincerely having issues with newbie coughing, advise that it is common among new vapors and will soon pass. It takes time for the body to adjust to vapor, just as it took it time to adjust to cigarette smoke.
It's also not necessary to inhale the vapor to absorb the nicotine; just suck on the device like one would suck on a milkshake, hold it in her mouth, and exhale through the nose and mouth. Also important to know that the nose assists the tongue to "taste" flavors in the vapor.
It's not necessary to quit cold turkey with vaping. I advise people to vape as much and as frequently as they wish, and when a cigarette craving comes along, vape even more frequently to overcome the craving. If that doesn't help, she may smoke half of a cigarette and save the rest for later. After a couple of days of steady vaping and occassional smoking with those partially smoked cigs, the cigs will start tasting pretty nasty. Remember, it's not just the cigs you smoke...it's the ones that you don't.
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Edit: I forgot to add...As much as I love my Provari and believe it is the best vaping device for ME, I don't believe it is a difference maker for the situation you have described. Proper vaping technique, the juice, and the right juice carrying device is more important in my opinion.