I would recommend you take her to a Dr...
At her age, it could be any number of things that's causing this - you want to start drawing blood and urine - checking if all of her organs are working as they should. H*ll... she could have Pheochromocytoma (a tumour that grows on the adrenal glands, causing unneccessary production of catecholamines) and you wouldn't have any idea, and nothing you would do then, would really help.
Draw blood,
Draw urin,
Give her a complete check-up
This is ultimately for the best, since this would help eliminate any other potential diseases she could have, which could give these symptoms. (there are MULTIPLE infections for instance, which really, no supplement will help with)
If possible, I would also do some form of neuroimaging on her, to see if there are any alterations to her brain. Alterations to her adrenals can often be diagnosed by a ultrasound btw.
Read more, in short, about neuroimaging and Alzheimers here:
https://www.radiolog...ease-evaluation
PET/CT - this scan seems the best, in early stage.
You don't want actual pharmaceutical drugs, but the drug I'd recommend (if she has high blood-pressure - check that) is GUANFACINE - ak a Intuniv or Tenex. It's an alpha-2-agonist, which lowers the activity of norepinephrine in the peripheral nervous system, while also lowering activity in the amygdala, as well as increasing activity in the frontal lobe, allowing for greater control of emotion.
It's commonly prescribed for the treatment of ADHD, which has some symptoms quite similar to early stage dementia - it was also specifically created to treat hypertension in ELDERLY patients, and is generally considered to be very, very safe.
If she's found to have the specific dementia called Alzheimers, then Memantine might help, if she's found to have frontal-lobe dementia, then Guanfacine might actually help initially, since it enhances function of the PFC.
You should also be aware that many modern-day drugs are derived from naturally occuring compounds... There's also the fact that "natural" remedies can be just as toxic - or do you consider the natural anaestethic, relaxer and painkiller, DART-FROG POISON as "non-toxic"?
For an actual supplement with this nmda-antagonist, soothing and memory-improving effects, look into MAGNESIUM-L-THREONATE - it's magnesium bonded to the amino-acid threonate - it's the first form of magnesium shown to actually have an effect on the brain.
She would need a significant dose, if it will have any effect.
If you want a herb with NMDA-antagonistic properties, then Polygala Tenuifolia will do the trick - it has multiple other effects, but those compounds are found in much, much smaller amounts than the nmda-antagonistic one.
You can find a thread about Polygala here on the forums, to learn more. It's used for irritated and congested noses in Chinese medicine - appears to have a long history of safe use.
And finally, for the most dangerous and irresponsible of treatments, you should have a look at your own LOCALLY AVAILABLE naturally occuring compounds - there's a plethora of them in the Brazilian jungle, you know... you probably live right next-door to the biggest pharmacy on Earth.
For instance, there's a spider, which lives in big nests, on your TELEPHONE POLES - it's poison is currently being researched for it's memory-enhancing properties - as far as I can tell, it's harmless in mammals - rats given high dosages are not badly affected. Humans are a lot bigger.
https://www.ncbi.nlm...les/PMC4522846/
Not sure if your grandmother is going to let you bite her with SPIDERS though... I imagine you would need multiple bites to get an effective dosage, since the spider-bite isn't classified as dangerous to humans.
And, never forget, what PARACELSUS, one of the wisest men whom have ever lived (and the creator of western medicine), once said:
"THE DOSAGE MAKES THE POSION."