As far as I know there is not enough sugar from the flavors or the juice: P.G., V.G., Glycerin getting into your system to affect blood sugar. It does metabolize into sugar in your system, but as we are not drinking it...
It has not affected mine and mine was wayyy out of control, now in control. It's the nic that's the problem. It affects blood pressure and other systems that are of concern to any diabetic. You need to talk to her Dr. and take the pictures of or a real e-cig. A list of ingrediants of nic juice and nic mg content and explain that she will only be inhaling "vapor"..NOT smoke. Nic is good for you BTW in tiny does, we all get some when we eat tomatos and potatos. P.G. is found in inhalers.
A brittle diabetic by definition is an out of control diabetic, by their own lack of control or because that is just the way it is no matter what you do. It's best to be very very careful of what you add or delete from their diet as anything can throw them into a serious medical state.
If her Dr. wants her off cigs, then the Dr. needs to be able to give her a way to do it that conforms to her habits and ability. Patches and pills don't do it.
Try explaining it like I did, I love chocolate, but a chocolate patch or pill won't help me quit because what I like is the way chocolate feels in my mouth, the scent, the flavors..not the chemical in chocolate!
Good Luck!