I'll post this comment seperately from the story comment.
I'm so glad you and your brother was able to be with her in her final moments. My Mom passed in 2014 and she was 90.I was the one family member that had the means to keep al day vigil which I did she was pretty much in a coma like state the last week but the staff assured me then she could hear me I am grateful I was able to be with her.Despite your Mother's dementia I'm certain she was aware of your presence and was grateful