Having (and still am) going through this with my mother a lot has to do with her age and abilities. My mom is 72 and not in great shape, with bad sight and very shaky hands. That rules out some setups right away as well as some techniques.
Because she has a choice in rehab of a patch vs a PV she went with the PV and I got her a very cheap (as in blister pack cheap) ego knock off with some CE4s, a couple of syringe topped bottles (no way she was not putting it in the center hole without the syringe to get the juice down the side) and went from there. I would have gotten her a more expensive set up but she drops things more than she holds on to them and her room has tile floors. The one I got I know from personal experience can take a beating and if she drops it enough (which she will - you won't believe the number of cell phones she goes through) to break it the replacement cost isn't something to whine about. I went with CE4's simple because they were cheap enough to be disposable and not have to face her with things like cleaning and maintenance and replacing heads, etc. Rinsing a CE$ and letting it air dry over night is just right for her.
She really wanted a 'cig like' set up but having to refill the tanks or the expense of pre-fills just were going to do it, although it probably would have made the switch easier for her because she likes the feel of a cigarette and the emphasis she can make with it in her hand when talking.
Just my opinion but I would start her out with a CE4 and then see how she does. Its a good starting place I think and give her some experience to work off of - deciding what she likes/does not like about it. That way you are not investing a bunch of money is something advanced and fancy that she sets aside and never uses or is too complicated for her. The CE4/CE5 does a great vape for what it is and while its not the epitome of the vaping experience it does a good job for the beginner and/or causal vaper, as well as being easy to use. You can always move up if it works out.
As for juice, thats so subjective. Some people find starting with a tobacco flavor the best way to go - others absolutely hate it and all ranges in between. This might be a really good use for buying a sample pack from a vendor that allows you to choose the flavors in the sample. I have seen them range from 5 bottles of 5 flavors up to 20 so you should have a good choice of different flavors for her to try. I started my mom on a 5 pack with a tobacco flavor, a drink flavor, a fruit flavor, a candy flavor and a 'bakery' flavor. Surprisingly she ended up liking the coffee flavor the best - thought she would go for the tobacco - so I am glad she had a choice. Turned out her second favorite was one I never liked (a candy flavor) so it goes to show how difficult is is to juice shop for someone else. Gift certificates please
AS for the diabetes I was a type 2 diabetic before I started vaping. Not claiming at all that vaping cured me but it improved my health and I lost weight and exercised a lot more and now have an AC1 of 5.5 (nondiabetic level) and am off all medication and diet etc. I don't know the risks with vaping and diabetes unless people are concerned about the sweeteners added (although most are not pure glucose but other natural sugars that diabetics use anyway as sugar replacers). If there are risks that you have read about I would really urge you to talk with her doctor about them before she takes up vaping because if it can impact her negatively that is not good. In my case the changes in my health were gradual but it did get to the point where I has episodes of low blood sugar because of the medication I was taking and I had to stop taking it. Myself, I never noticed blood sugar spikes related to vaping and at one point I was testing regularly 8 times a day - around a great deal of vaping. Everyone is different as is how things impact them so its worth being vigilant and getting some medical advice or at least letting the doctor know what changes she is going to be making.
