My grandmother is already a senior and she has this thing where you have to be careful what you say and how you say it, one wrong word and she thinks you're angry at her! Also she tends to make up stories of family members that aren't true, it ranges from accusing one of being uncooperative to one being aggressive with her, I have bipolar depression and she's constantly not picking at me but can't say nothing due to the fact that she takes it as aggression.
Also, an urinary tract infection can mimic dementia, so have someone take Grandmother to her family doctor or to an Urgent Care where a test can be done. The treatment is antibiotics.
Within a few days of antibiotics she was nicer.