I was just a bit worried because from what I have deduced from lots of reading on forums.
It seems that 1ml of 18mg e-liquid equates to about 7 legacy cigarettes.
I was pleased that she had been using the equivalent of 11 or 12 legacy cigarettes which was close to her 12 or so a day before starting to vape.
Now she is exceeding that "equivalency", if the information I have found is close to accurate.
Truly, there's no way to really work out a proper equivalency - it all depends on your equipment, how you vape, etc. As I said, I wouldn't even give it a second thought unless you had good reason to think she had a health problem which was aggravated by nicotine. I smoked a pack a day, and by your calculations I would be smoking a gazillion packs LOL Obviously my overall improved health begs otherwise! There's a lot of misinformation on the forums...