Borderline Narcissistic 92 yo mom with dementia in denial of her decline: nothing is ever enough. How do I deal without going insane?

This is my first post.

My mom is about to turn 92. She has BPD and NPD and has her entire life. Everything she is now in terms of her narcissism and borderline is a more extreme version of the way she always was when my sister and I were little kids. I am her sole caretaker -- my sister lives 3,000 miles away and hates her guts for good reason. She's paranoid and delusional and extremely tightfisted.

I started taking care of my mom 20 years ago. I didn't think she would live this long. Every year, she gets more difficult to deal with. She's delusional, paranoid, hypercritical and demanding. She's a hoarder living in a two bedroom apartment who is only not buried because she got bedbugs six years ago and had to get rid of everything she owned.

She moved into assisted living four years ago and moved out back to her apartment after seventeen months. Between the fact that the other women there were incredibly cruel to her and the fact that after she broke her hip, I had to go there every single day for six weeks because no one went and saw her except for the people doling out her pills. I thought it would be easier for her to move back to her apartment, three miles away from me in a building with a concierge instead of me driving 12 miles each way. The maid from assisted living was cleaning her apartment weekly until, true to form, my mother fired her at Christmas, despite the woman having found her when she fell in AL and having saved her life.

She has severe osteoporosis, congestive heart failure, a pacemaker. She's colonized with antibiotic resistant E. coli and is incontinent. She cannot and does not clean up after herself but NEVER has. Her apartment is a disaster and she keeps saying she has to "get someone in here" but literally no one will put up with the way she treats people. Six years ago, someone who knew my sister and BIL came her to take care of her full time and be her maid. She was so nasty to him that he would go lock himself in the bedroom and cry and told my husband that people were nicer to him when he was in jail than my mother was, since she verbally abuses anyone and everyone at will. She's completely self-centered and disinterested in anyone else's well-being.

Recently, her short term memory and word recall are just shot. I'm not talking about complex, low frequency words. She couldn't remember my niece's name and calls her "the older one." She couldn't remember amazon.com, despite ranting about it and Jeff Bezos for years. She forgot my 17 year old daughter's existence. She'll ask me a question and then ask me exactly the same question two minutes later six or ten times in a row. She confabulates like crazy all the time til my eyes are rolling around in my head as she retells stories from my childhood saying they happened to her or that she was there when she was not.

Her affairs are beyond her ability to manage them. She gets mail and never opens it because she's angry at the sender, she loses envelopes with important documents. She has a house she's renting out that she wants to get rid of the tenants in the middle of the pandemic so I can drive her there forty times in the next three months arranging things with tradesmen to repair it because she can't get along with anyone ever. I am her entire social life. She has very high social needs.

I call her daily since April 1, I do her marketing but that's not enough: she's angry that I don't see her 3x/wk, because according to her, I do virtually nothing for her. She has NO friends. Her siblings are all dead. None were on speaking terms w/her for years before they died. She wasn't allowed to go to their funerals or even notified of their deaths until years afterward. I haven't seen or spoken to my cousins since I was in high school because she antagonized her siblings so much.

Advice from those who have been there done that?
How can I sort this mess out before she doesn't know her name anymore? Her mental illness does not make her incompetent.