I agree about cutting down the nicotine level and remember, vaping does leave you mouth on the dry side so you do need to drink when you vape. I also experienced coughing when I started vaping, I coughed for about 3 weeks and then it stopped.
It also may be possible that a 510 is too much for your wife, perhaps she would enjoy the lighter vape of a 801. When I started vaping I tried a 901 first and ljked it pretty much, I then started exploring the virtues of the 801 and the 510. You might want to get some adapters like 510>901 and 510>801 and get some of these attys so that you wife can try the different tastes of each on your 3.7v battery.
Also tell her how much you love her and want her to be around for a Long time. Tell her about the health benefits and the cost savings as opposed to buying analogs. Also, if you have kids, how much better it will be for them not to have to breath in that secondhand smoke. Not have a stinky house and car. Be able to enjoy a nice vape after a meal in a restaurant. ETC