My prayers are with you, Marty!
Has it been possible for you to take your mother to her family doctor for a thorough physical examination (to rule out any possible physical causes of her hallucinations), be referred to a neurologist for a thorough neurological examination (to determine whether she displays the warning signs of Alzheimer's)? Is the assisted living center where she resides, a secured building with special security entrance/exit codes? Are her medications administered by someone other than herself (such as a nursing staff member at the assisted living center)?
Since your mother appears very lucid as to her finances, she may probably recall short sequences of numbers, such as the entrance/exit codes. Concern for the possibility that she may wander is very much a top priority. There are special bracelets that she could wear, that would identify her, in case she wanders. I am not certain if any have "tracking devices" to know where she is at all times.
As a registered nurse with over 20 years of experience in long-term care, I am now a "new baby" in the role of care for my 81 year-old mother (who needs to be assessed/evaluated, but denies she has any need!!!). I am her power of attorney for healthcare, and live about 100 miles from her. No other siblings survive. Her personality changes are of greatest concern, and I have found an excellent assisted living facility in the city where I reside. She is very aware of her surroundings, however, I believe the denial is probably her fear of losing independent living.
Do you have an Alzheimer's support group in your area. Ours is EXCEPTIONALLY WONDERFUL.
I know that if my daughter and I go to Mom's and take her to the car, she may show great resistance, and the neighbors will wonder what in the world is happening. Mother does not share important details (such as the name of her current doctor, etc.).
I wish you well, and I'll check this site for any concerns you may have.