You can get vape juice that is 100% VG (Vegetable glycerin) This will reduce the need to cough. PG Propylene Glycol is what gives u the feeling in the back of your throat. Generally Juice is 80/20 or 70/30 80 VG and 20 PG. the 100% VG doesnt taste as good as the 80/20 from what I've been told. I've only used 80/20. Another thing that causes coughing with vapes is if people hit them like they do a cig. to hit a vape you should put your whole mouth around the end and inhale without any extra air. I know most people that start vaping cough a lot at first. Just have her take it easy until her throat is used to the vapor.