I hope you do not mind my commenting. I always thought my Mom's side of my family (I am 57 she has passed) struggled with early onset dementia and alzheimers. I went through early menopause, as did they, at age 39. For a long time I thought I had and the doctors thought I had psych problems, depression and/or anxiety. Out of desperation I went to a naturopath about 10 years ago who diagnosed a very severe Vitamin D deficiency. A couple of years ago I was diagnosed with Hashimoto's Disease, which is thyroid related. I take two thyroid meds every day, Vit D, A, Iron and Zinc, and a few other things. I am now in remission and feel better than I have in about 20 years.
The thyroid gland produces 2 thyroid hormones, t4 and t3. t4 is converted to T3 and only t3 is used by the body. For a lot of reasons, the conversion mechanism can slow down or break. People with low t3 and free t3 are likely to have mental health symptoms, even mimicing dementia and alzheimers. You might want to check if she has had a full thyroid panel done, including Free T3 and Total T3. So many vitamins, minerals, etc affect the thyroid. Maybe she would be more open to a Naturopathic type of a doctor.
I was so grateful to have found a diagnosis and this information about my family's health history. I believe my Mom and her sisters had undiagnosed thyroid problems. People who have European ancestry have a genetic predisposition to it.
I am hoping the above might be helpful to you in some way.