Sorry to hear about your family troubles. Every case of senility-related dementia manifests itself differently, so my personal experience may not apply...
My Dad suffered from senile dementia--very different from Alzheimer's disease--the last 3-4 years. Strangely, although he was "diagnosed" by his doctor as having Alzheimer's, he never descended into the profound dementia characterized by anger, confusion, inability to recognize friends and family. It was a progressive decline in mental acuity but certainly not in a linear fashion. He had some very good days and some bad days that became increasingly difficult to adjust to. However, the last few years with Dad were some of the most fun times we had since I grew up and started out on my own.
I was pretty independent as a kid, dropping out of college at 19 (much to Dad's chagrin), moving out of the house, getting married, having a family and a mortgage by the time I was 21. To say he wasn't exactly thrilled with my life choices is an understatement. We weren't estranged by any means but we each went our own way for 45 years, until his diagnosis. In the last few years, I made extra efforts to spend time with Dad at least once a week, stopping by his house (he was still living at home with his wife) and taking him out to lunch to have a burger and a beer...or two. What was most noticeable was that as his senility progressed into his 90s, he left behind much of the "shell" that we all surround ourselves with and show to the people we associate with. There was no pretention left, no judgement made, no approbation--just the basic person he was inside, which was a kindly old man who loved his social interactions and his family. He was an absolute joy to be around and interact with. Now to be fair, having a conversation could be maddening: much like you describe with your mom, he would ask the same questions over and over. At first, the question was repeated every 5-10 minutes, but as his memory progressively failed, he would repeat himself every 60-90 seconds. It was almost as if he was trying to imprint the question and answer--which he must have felt to be important--in his brain. The information sometimes finally stuck, sometimes not, but he was always pleased to be sharing conversation with me.
Bottom line, you and your mom are on a journey that will undoubtedly lead to her final days. You'll see her at her best and her worst, but cherish the time you have with her. As she fades into her dementia, you'll likely learn something from her about the impermanence and fragility of life...which is a very valuable insight into how you should live the rest or your life! Sending you my best wishes and hoping you find that large well of patience to deal with her disease.