How can I get my mother the help she needs?

My mother is 75, had a stroke about 10 years ago. She still functions fairly well in some ways.
She lives in her own apartment, remembers when her rent, electric and phone bills are due. She balances her checkbook just fine, remembers when she has appointments, etc. She is not driving at the moment because I turned her in to the Secretary of State after she'd gotten lost several times in the area (within 5 miles of her apartment) and admitted she'd driven through red lights several times because she blanked out on the road. The Secretary of State tested her twice and she failed each time so she can't drive at the moment.
She has some health problems -- high blood pressure, diabetes, some mental decline, back trouble, hard time walking and she still smokes three packs of cigarettes a day, which isn't helping her mind or body, obviously.
The most alarming problem is her mental state. She has some problems mentioning the odd word or can't really understand her cell phone very well. On one hand she's never been terribly focused -- she wouldn't bother to remember neighbors' names or even that the channel she watches most on TV is PBS, but that's nothing new with her.
What is newer, however, is this psychotic paranoia. She is convinced she's around the worst people. Over the last 10 years every neighbor she's had -- this is about the fourth one out of three houses/apartments since 1996. Every last one has been a criminal of some sort -- according to her. One was a drug dealer, two were prostitutes, and another was some sort of scammer.
She has other strange issues, too. She's 75 but thinks she's quite the looker and thinks men in their 20s and 30s are falling in love with her, even fighting for her affections.
She also thinks my husband and I steal from her. Once I brought in groceries and put a multi-pack of paper towels on top of her fridge and she told me I was scum to steal that from her. When she finally found them her reply to me was "that's not where I put them," and not "I'm sorry I accused you of stealing."
She thinks my husband is stealing her valuables, but by valuables she means knick-knacks, like a horse figurine or an old angel figurine. She is convinced my husband is hoarding her stuff so he can leave me or if I die, and then he can sell this stuff and start anew. The stuff she thinks he is stealing isn't even valuable -- she wouldn't get $10 for it at a yard sale -- never mind that she's accusing my husband of stealing!
Once she hid $500 and couldn't find it and said he'd broken into her apartment while I took her shopping -- he seriously is going to leave work and break into her place to find hidden stuff? -- and found it and took it. Eventually she did find the money and admitted it. I'd hoped this cleared the problem but then she started up anew about how convinced she was he stole her home decor.
I've spoken to her doctor and even to a psychiatrist when she had an episode when she was hospitalized for a bad urinary tract infection; during her recovery she had psychotic episodes. She passed the consultation enough by knowing what the date was, etc. and the psychiatrist said it would be nearly impossible to commit her or force her to take help.
She refuses to do anything that would improve her mental or physical state. She stays in her apartment for days on end, barely bathes, refuses to quit or even cut back on smoking, eats one meal a day and drinks only lemon-lime soda (even though she's diabetic and has been told repeatedly that it's not a good diet for her), won't consider a hearing aid even though she has horrible hearing loss. (She thought one neighbor worked in a coffee shop when he worked in a home decor store; we're not even sure how that happened!)
If she doesn't get her way -- cigarettes by noon, if she is low, for example -- she threatens suicide.
With the drama and accusations, I don't know what to do anymore. She is hostile to my husband and me -- she had her locks changed so we can't even open her doors to drop off groceries -- and she gave us our house keys back, so she obviously doesn't want to visit us either. I can't get her any help, and she's cut us off more and more. Friends have tried to reason with her not to cut off her last remaining family -- she cut off her two sisters and brothers years ago, and all nieces and nephews. I don't know what to do, or if I can do anything. Does anyone have any advice? Can I force her to get on antipsychotics or possibly push her into assisted living or a nursing home? I don't even know what the next step should be. Any advice is welcome and appreciated!