1. Head over to the Health forums here. There's a lot of psuedo-science, justifications, actual science, gems of information, and often most useful of all -- people's experiences, even if people don't have answers. There is a lot of good dental related information there. Don't expect definitive answers -- you will have to piece some things together.
2. Teeth are awful things. It would be a dream if we were born with a care package that has six extra sets, but we unfortunately that isn't the case. We only get one set. Like sidetrack mentioned, it could be one of many things, vaping exacerbating one of them, or one alone, especially as we age.
3. Have her see the Dentist. Either way, if you have a heavy level of enamel wear, you will find a ton of things sensitive or almost painful, or straight up "Ouch!" Same goes for cracks, fillings, cavities, dry mouth and everything in between. It can be as simple as something cold or hot - ice water or coffee. It can present itself always or sometimes.
4. Taking the fact that we only get one set....even the simple sometimes "strained" motion of vaping, the general airflow, the general loss of moisture simply from the motion without actually vaping can cause sensitivity, like trying to drink too hard out of a small straw, like trying to puff off an imaginary Provari when funds are low or someone trying to whistle for the first time. If there's any existing condition that sort of dry draw is a tooth's enemy. When you tack on the ideas of dehydration and vaping, you'll have a dentist applauding you for quitting smoking and eventually crying when they start thinking about dry mouth.
5. The dehydration thing - to me this is less about "didn't drink much water, I felt weak", this is more about "your mouth needs constant care and feeding", period.
I'm a person that prior to vaping wasn't a big water drinker. Just wasn't on my mind. When I'd drink water, a light would switch on and I'd want a gallon. My significant other is the total opposite. She drinks water through the day like she lives in the Sahara. The first time I started caring that much more about water was shortly before I began vaping -- I screwed up my back while hiking and was given pain killers for two weeks. The doctor warned me about the normal stuff, but really, really stressed the dehydration factor to the point that I asked more questions.
I assumed it was about things like dizziness and the like, and but focused on dental issues...so much about maintaining a balance of things in regard to teeth and the mouth that I asked more. I'd never really equated the impact of taking meds with an impact on teeth. I ended up learned more than I wanted to, but enough to scare the crap out of me. All I can say is have a strong stomach if you start web searching about dry mouth and the effects.... I think of vaping in a similar but probably stronger manner than the way some medications can affect the mouth....and thus the teeth.
I have had sensitivity here or there during my short stint in vaping. I do find it slightly more with the metal drip tips -- I think this is more to do with the fact that I hold it in a less relaxed, more strained way than the more open Delran's I have or some of the softer, more forgiving tips that people included as a freebie.
The fact that my SO mentioned similar things in the last week after about three months of vaping and less than me made me worry a bit more, especially for someone that is and has always been someone that would get ten gold stars more than me regarding dental care.
I also subscribe to the idea of more frequent brushing with a very soft bristle brush. Nothing excessive, but I can't help but think that my teeth aren't to some extent either coated with PG or VG....or worse....dry. I've also sworn away from the typical Mouth Washes like Listorene...or anything Alcohol based that further dries out your mouth.
6. But despite the wall of words above, the short answer is get her to the dentist. With or without, head over to the health forums here. But also browse around a little bit for brands like Biotene and Oasis, whether it be Amazon or the local grocery store. There's a ton of products meant for mouth dry mouth but also sensitive teeth -- toothpaste, rinse, spray, gum, the whole nine.
When I had the brief sensitivity stint that could border on being called pain, a few things helped me - (a) Advil, (b) Crest Sensitivity toothpaste (a godsend really), (c) a couple of the small tooth pain products (things like Ambesol but in a gel form - I forget the brand).
My random guess though -- which is about as useful as anyone else's comment unless they are a card-carrying Dentist -- it's probably vaping exacerbating an existing condition. But always keep in mind that even if it amplifies an existing condition, it isn't to say that it isn't also making it worse.
Either way -- same as everything else -- try to make the most informed decision you can make and if you find a Eureka moment, or gem of knowledge please, please, please share it with the rest of us. It's for the benefit of not just your Mom, but all of us.