If she finds flavors like JC Hexport to be too sweet, then she's just going to have to accept that vaping is different than smoking. PG (and VG) naturally has a slightly sweet taste to it. Juices like Hexport and Dumay were not designed to be sweet, so finding something LESS sweet will be quite the challenge.
You may have better luck reducing the sweetness by using a higher wattage set up. Either LR atomizers/cartomizers, or a high/vari-volt device can make it taste a little harsher, often in a good way. Another option is to try the tank system. I find it to be a drier vape, and the flavors are muted.
Remind her that very few people like the taste of a cigarette the first time they try it. There is an adjustment period just like there was when smoking. Moreover, there are many different set ups and juice combinations. It takes time to find something that hits the nail on the head for different people.