I think there are two factors with vaping that might affect blood sugar: nicotine and vegetable glycerin. The effect of nicotine on blood sugar has been known for quite a while, and considering that she's already a smoker it's more or less irrelevant unless she winds up vaping more than she ever smoked.
Vegetable glycerin is more iffy. Nothing conclusive has been done, but there are things that suggest it may have more of an effect on blood sugar than typically thought. The variation in people using vegetable-glycerin-based versus propylene-gycol-based juice would explain the anecdotes of some having blood sugar issues after vaping and some not. This is largely guesswork on my part, of course. Still, you might want to use propylene glycol, or consider it if switching to vaping seems to be making things worse.
