Having a hard time getting help for mom. How can I help her when she refuses?

I feel like I'm getting nowhere with help for my mom. She has signs of dementia -- paranoia, confusion, etc., plus is hard of hearing.
She refuses to get any medical help except to see her primary care doctor. She won't see a heart specialist, a neurologist, neurologist, etc. It's always too expensive, she says, even though she has a decent pension.
While she has issues with confusion and so on she is clear enough (for now) to know when her rent, etc., is due. Due to the dementia, though, I'd like to get her more help. However, I call the area on aging and they say I might want to try the courts. I call the courts and they say I need something from my mom's doctor. I try mom mom's doctor, and she says to try the area on aging.
I really suspect my mom's doctor doesn't believe my mom needs additional help. My mom has some personality disorder issues -- a textbook narcissist, for starters -- and she can play "normal" to get out of any real scrutiny.
My mom's effectively locked me out of her life -- changed her locks, etc., accuses me of things that never happened, and if I try and get around these accusations I'm a liar or have bad memory. Basically all she wants is someone to come around and nod at whatever she says and to praise her and take her shopping when she wants -- my work schedule means nothing, and so on. She needs it now and that's that.
My mom's doctor suggested I go to the area agency on aging to find someone to hire to help my mom. Thing is, I've tried that before: After her stroke a decade ago I had a nurse come by for therapy; my mom fired her after a week because she didn't like the look of the woman. Other times I've hired help for chores and she fires them after a few days, too, and it's always something like they talk too much or they have a weird laugh. (And I'm the only one who gets to hear all this stuff; she'd never be honest with anyone else.)
I'm at the end of my rope here. My mom's doctor is no help, and my mom wants little to nothing to do with me (and she's cut herself off from the rest of her family over the last two decades so I'm effectively alone in terms of family in this because I got tangled up in all her feuds) and in the past when I've gotten a psychiatrist to check her out (at the hospital for a different medical matter) he even said it'd be near impossible to commit her because she was answering all the questions correctly.
On one hand I'm tempted to wash my hands of the whole matter since I've been coping with more than half my life of being belittled by her for everything from where I hang my pictures on my walls to how I wear my hair to how I dress to how I answer the phone (basically if I'm not a carbon copy of her and her yes-person, I'm dirt).
On the other hand, she is my mother and I feel obligated to care for her. I'm at a loss. How do I help someone who is mentally ill, has aging issues, and who knows how to play "normal" when she feels her survival and status-quo are at stake?