86 year-old mother's worsening bad breath

I have not posted in a while.
( I actually got into affordable housing for six months, and it was such an unhealthy, traumatizing environment, that I ended up right back here to just to breath clean air and feel safe. I was also finally diagnosed with autism spectrum disorder. I am currently looking for a normal apartment and will use my disability account savings and hope it doesn't run out before she dies and leaves me her house.)
One of the worst things now about being back here, is my mother's worsening breath over the last so many months. She says she brushes her teeth and gets regular cleanings, but her breath smells like mothballs (or plaque) and possibly something else I can't figure out.
It's mostly when she talks or just breaths. Her breath fills up about three feet or so of space. If she is on her computer in her office, I cannot go in there because the whole room smells. I am literally unable to be close to her because it makes me want to throw up. It's becoming really disturbing.
As someone with autism, this is a sensory nightmare for me. I've been hunting for the little scented plastic nose ring I bought that will help mask the odor.
I do not think she always brushes her teeth as she often falls asleep on the couch with her mouth side open, and then gets up in the morning and gets busy enough that she forgets to eat or drink water, so I am wondering if she is brushing as much as she says... I bought her dry mouth lozenges but she doesn't use them enough. I am going to buy some mints she likes and leave them on the counter as a way to encourage her to use them more often.
Either way, I am beginning to think that the bad breath is more systemic than just poor oral hygiene. She is 86 and eats a lot of sugar at night on an empty stomach, doesn't drink enough water at high altitude here, and isn't looking so well - kind of pale and face sunken in more than usual.
I have told her a couple of times that maybe she needs to get a workup, but she doesn't bother. I really cannot say much to her because she gets defensive and that is triggering for my mental health. She has a personality disorder with OCD and unchecked anxiety. I never know when a normal conversation is going to go sideways. I walk on eggshells a lot.
I have been reading that bad breath can be caused by a number of things, but if I can smell it and it lingers when she is just talking, then it may be systemic - like unprocessed waste being filtered back and out through her lungs.
Has anyone else dealt with this? My grandmother lived to be 102 and had bad breath, but it was more plaque, and didn't project into the air three feet in front of her.
** I am back to trying to stay away from her for other reasons in spite of the enmeshed relationship she always tries to have with me. She does rely on me a lot more these days and I am happy to help, but maybe the bad breath is a reminder to stay away as much as possible because of the smell. At least soon I will not be living here full time and just working at my home business out of here because she has the space for all of my books I sell.
I have to admit that I am totally over dealing with her for the most part. I love my mother, but she has treated me like crap, and if the yelling is going to come with bad breath, that at least makes me walk away much faster rather than stand and defend myself, which is something I am still working on.