How do I get over the anger that I have for my mother?

My 92-year-old mother is a narcissist and is now living with me and my family until her home is repaired after a fire. It has taken much longer than expected. My mother insults my husband and children and then acts as if she never did or said anything when called on it. She has always been verbally abusive to my brother and myself our entire lives but she puts on the "I'm a great mom." act to everyone. My brother has hands off the whole situation and does not visit or call because he does not want interaction with our mother. I am the one who everything falls on. I pay her bills, conduct all business as far as getting the house repaired, take care of her in my home and it is all so overwhelming. Sometimes, I find myself so angry at her that I cannot even look at her. She is insulting one moment and acting as if she didn't do or say anything bad the next minute. I'm sure she has dementia, but will not see a doctor for this as "someone will want to put her in the nursing home". She also is very paranoid about people, including me, stealing from her and money is always missing and she points to my husband as the culprit. She does not want to keep herself clean, wants to reuse diapers and literally has the upstairs of my home smelling so foul it is almost too much to take. I realize that most of what I feel about her is because she always made everything about what girls are supposed to do. So growing up I was made to do everything, cook, clean, etc.,while my brother received a free pass. So this is still the issue today. She is never grateful for anything I do for her because I'm supposed to do it. Although her house will be finished soon I know that she technically should not go back there as she cannot take care of herself. She is so frugal with her money that she will not pay for help with her needs when she does go back home and I do live in another state. She will not complete a will and she does have modest assets, which includes the house and savings. I would want to see her use the money for herself, but she is obsessed with saving it. All these things are so frustrating and a big strain on my 30-year marriage and for my 14-year-old daughter. Even when she is back in her own home I can only see it getting worse as she will want me to be at her beck and call even from another state.