What do I do to help my 83-year-old mother who refuses to help herself and go to the doctors?

My mother is a diabetic who in the past 6 months or so doesn't even check her sugar levels, she has neuropathy, kidney problems, heart problems, high blood pressure, shortness of breath, doesn't eat right, refuses to go back and see any of here doctors in the past year in a half, who still continue to fill all her prescriptions, sits in a chair all day and night and sleeps, will not move out of her house or let anyway in because she doesn't want them to see how she's living, and expects me to continuously come out and clean her house, do her yard work (2 acres of mowing) and do all her necessary errands, and that still isn't enough. I have a brother who comes out several times a year but she doesn't expect him to come out and share the responsibility, and we do not communicate. She is terribly depressed and complains but won't do anything to help herself. She was robbed twice and tied up while the robber ransacked her house, but she managed to set herself free and run for her safety a few years back, and she has never gotten an alarm or done anything more to secure her safety. She has alienated herself from whatever friends she has left because they preach to her. She gets out to play Bingo a couple times a week, but then six months or so she couldn't figure how to turn on the headlights to her car and when she drove home she sideswiped her car on the expressway when the other cars close to her passed and she was in complete darkness. She lies and plays games and won't answer her phone if she doesn't feel like it. I've done everything in my power to try to get her to move into an assisted living and go see a doctor and she refuses. I have not spoken to her in two weeks now and feel guilty but she's stresses me out so much that I feel I need to take a break for my own sanity, but yet I feel guilty and sad for her. Can anyone give me any sound advice?