How do I handle my aging Mom?

This is long, and I'm very stressed out, so please bear with me. I am an only child, and my mother and I haven't been able to get along since I was about 12 years old. I'm 64 now. So much so, that I moved away from my home town when I was 19 and haven't lived here since. I just recently divorced and in July I moved back home, and I have moved into a rental house my mother owns just across the street from where she lives. She has given me a reduced rental rate.

Ok, here is the current problem. My mother is suffering from the beginning stages of Alzheimers or Dementia. She becomes confused, frustrated, she is very forgetful, very angry, no memory to speak of. She has always been a mean, hateful, revengeful, vindictive, controlling, and bossy person; especially to me. I get the full bore of her. My mother has no business driving whatsoever !!!! She is going to kill herself or someone else !!!! This being able to drive thing is a very big deal to her. Her husband (not my father) is totally blind, and he doesn't help the issue because I'm sure he wants her to continue to drive as she is also his taxi.

I have become sooooo concerned about her driving that I attempted several times to talk to her about this to no avail. She becomes soooooo angry and mean to me that it is useless talking to her about this. So I wrote a letter to our state DMV office complaining about this. I spoke with my daughter before I wrote the letter asking her if I could sign her name to this letter, as the ramifications would be less if I didn't sign my name to this letter. She received this letter abour 1-1/2 weeks ago, and saying "something" hit the fan is an extreme understatement. The letter told her she needed to take a physical driving test, a written test and a vision test at her local DMV, she also has to go see a dr, and get a physical report from her dr, and she must go to a vision center and have her eyes examined and submit this report to the DMV as well by October 28th. If she fails any of these tests or doesn't comply she will lose her driving privleges. My mother has accused me of either writing the letter and signing it OR writing the letter and having someone else sign it. She went so far as to (only in this small town) drive herself down to the police station and she talked them into calling the DMV and asking them who signed the letter. She couldn't do that as she can't see the buttons well enough on the phone to call herself. So the DMV did tell the police that my daughter signed this letter. My mother went ballistic. I have denied everything so far. Now, I find out that she has written a letter to the DMV requesting they send her a copy of the letter thart was written to them because she thinks she can recognize my handwriting. When I found that out from a support person who talks to my mother and step dad I just about lost it. I went into a complete meltdown because I knew then that I was busted and she would never forgive me for this. See my mother wouldn't see that I did this out of love and concern for her, oh no, she would see it as I was causing massive problems for her. So, while sobbing I called the DMV office and asked if there was any way they could not send her a copy of the letter I sent and I was told no, they would have to send it to her. I was then told that I could email them a note saying I was withdrawing the request for her to be re-evaluated, they then would shred any and all paperwork pertaining to her case. They would then send her a letter stating that the person who basically turned her in had withdrew their request. I told them to do this. My mother is sooooooooo angry at me that she INDEED may disown/disinherit me. The person I lean on for support who knows my mother well has stated that yes, this indeed may happen. My mom will never know who wrote this letter to the DMV, but she will have her suspisions. What/where do I go from here. Honestly I don't ever want to go to her home again. I know I should't feel this way. How do I deal with her accusations, her anger, her hate, her revenge. She could honestly attempt to have me evicted as well. If she disowns me, and I can find out by going to the courthouse and looking at the public records, do I move away, never to step foot here again, or speak to her again. This is soooooo difficult for me. I love my mother, but the love I feel for her comes from the memories I have as a very young girl. I had the best young childhood up until I was abourt 12, then everything went down the toilet and since then we don't get along at all. What do I do from here? I'm told that this will only get worse, how do people handle these kinds of issues. She told me she doesn't want my help, and all I'm trying to do is take over her life. I AM NOT trying to take over her life. I just thought by being here, close by I could help her, but apparently she doesn't want my help. WHAT DO I DO ??? Thanks for reading !