Mother has disowned me, refuses to see or talk with me, but needs much help. How will I be able to help?

Hello, this is my first time posting here, though I refer to this forum and find it tremendously helpful! My mother is 80 and still lives with my father at home. In the past 5 years we have noted a marked progression of memory issues with her. In the past year it has escalated to now involve her behavior and emotions. She has become increasingly suspicious, angry, and now even paranoid. Though she's never been diagnosed with anything she checks off on at least 7 of the 10 warning signs for Alzheimers. We have spent the past few years trying to get her in for testing and diagnosis but she refuses and is in deep denial. In the meantime my father and I have learned to do our best not to argue with her, even to the point of letting her rage and rant at us with very hurtful language while we just bow our heads and apologize for whatever it is that set her off, no matter how random. In recent months she has had a few near-miss car accidents. She and my father had planned to make the 2-hour drive over a mountain pass to spend Christmas with my family, as well as my sister and her family. But something triggered her rage before the trip and she refused to drive with my father over the pass, insisting she would drive herself over in her own car the next day. But we are all very concerned about the potential for her to get into an accident. My dad did not know what to do, but didn't want to upset her anymore so he agreed to drive himself over and let her have her way. At this point I intervened and came up with a (fake) story about how I needed to come stay with her the night before she planned to leave, hoping to persuade her to drive with me back over the pass. She insisted she wanted to be in her own car but agreed to let me drive behind her. Just before the pass we pulled into a small town for a bite to eat. I watched in horror as she pulled out in front of a speeding truck, a very close call. I asked her if she had seen the truck. She defiantly claimed it was all 'his fault' and did not seem fazed. Then she got very agitated with me, insisting she no longer wanted me following her. I tried to persuade but she only got angrier, so I agreed but then left first and hid my car so I could pull out behind her and still follow. Unfortunately it was now dark out, and the heavy traffic and rainfall caused me to lose her on the road. There was nothing I could do but drive on, full of worry and concern. This is when I made a bad decision. I drove to their townhome and decided to wait for her to arrive. I waited for 40 minutes out in the parking lot as I didn't want to go inside and worry my dad. But the longer I waited the more I worried. By the time she pulled in I was ready with my "speech." My dad and I have always been very gentle with her, but after so many years of her resistance to help, her increasing rage and anger, and the ever-increasing need for medical intervention and worry for her safety on the road, I thought I might try my sister's suggestion to be more firm and forceful with her. Bad idea! Though my speech to her was along the lines of "we love you and are concerned for you and your safety and want you to accept our help" it was delivered with a raised voice. To make matters worse, I used a few angry "LISTEN to me!" and pounded my fist on the counter to get her attention. She had a complete meltdown, screaming that I was the most hateful daughter in the world, that no one has ever been treated as horribly as this, that my dad had put me up to this (he hadn't, and in fact would have insisted that I just let it go), that my dad had turned the whole family against her. As her rage went on she started to form a new story, accusing me of wanting to kill her, that she would just go ahead and "do it herself". Then she grabbed her purse and keys and tried to leave. Being very worried now about her safety I used my body as a block so she couldn't leave. She pushed at me to get past, and I had to push back some so I wouldn't fall down. My raised voice lasted only the first few minutes, but the rest of the 20 minutes or so of the episode I was calm and repeating "I love you, I'm worried for you", even as she raged and pushed to get past me. Once it was clear she was not going to leave the house I sat down and continued with calm loving words, recalling happy memories with her, but to no avail. She now insists she never wants to see or talk with me again. The thing is, I am her power of attorney and main caretaker after my dad (who has his own aging concerns which I also look after -- happily, I might add). Although her behavior will definitely put a damper on the holidays (she will not come to my house for the annual gathering), what concerns me most is how will I be able to help when she refuses to have contact with me? We had planned to move them closer next year, and the logistics of a move won't happen without my help, not to mention all the other matters that she will need help with. Help!