What Are The Symptoms Of Dementia?

My 86 year old mother who lives with us has started biting her nails really deep (3-4 months now), is losing her hearing more every month, and has been dry-coughing a lot. She was recently diagnosed with mild a-fib, and given a new med to raise her low BP. She is on kidney hemo-dialysis (for 3 years now) . Today at a restaurant, she just went to an empty table and had a seat, even though my brother told her that wasn t our table and there was plenty of seating in the waiting area (I was in the restroom myself, couldn t intervene). I wonder if she HEARD by brother, or she is just starting to exhibit dementia.