It sounds as though your mother has probably always suffered from anxiety, but it sounds as though she's really going on the deep end---even for a Witness. I don't think she has Alzheimers or Dementia, as those diseases make you forget things. It sounds more like she could becoming schizophrenic. I found some of the warning signs:
Negative symptoms generally include apathy or lack of motivation, self-neglect (such as not bathing), and reduced or inappropriate emotion (such as becoming angry with strangers). Negative symptoms usually appear first and may be confused with depression, and later with other conditions such as substance abuse or bipolar disorder. 1
Positive symptoms, which generally appear later, include symptoms such as hallucinations, delusions, and disorganized or confusing thoughts and speech. Symptoms of schizophrenia usually emerge in adolescence or early adulthood. Symptoms can appear suddenly or may develop gradually, often causing the illness to go unrecognized until it is in an advanced stage when it is more difficult to treat.
Schizophrenia is diagnosed primarily with a medical history and a mental health assessment. Other tests, such as imaging tests (including a CT scan or MRI), blood tests, and physical exam, may be done to rule out other conditions that can mimic symptoms of schizophrenia.
I know you've said she will not allow a doctor to examine her, but there comes a time where you or a sibling will have to step in and force the issue. When someone can no longer make rational decisions for themselves, someone has to step in. This happened with my grandmother. She was getting dementia and refused to let the doctor examine her. After much nagging, I finally got my aunt to take her to the doctors as she had Power of Attorney. There's all kinds of laws that step in with people who are no longer working on all thrusters. It sounds like this is a prime example. She needs to be examined thoroughly before she ends up harming herself or someone else.