I think a lot of people think this is easier to stay disengaged from than it is. My parents said for years that they would move near me, move into a senior living community, etc. and do their best to never be a burden. Then they started to get to the point where they needed help and their tune changed. For the most part, while still trying to respectful I have ignored many of their current wishes and gone with things that I knew they had always said they wanted. Getting them home help kept failing (they would fire whoever I hired) so I pushed hard to get them moved into a place, got rid of their car, took over their finances, etc. I could have left them to fail, but the cost would have been very high. They literally could have killed someone in the car, given away all their money, burned their house down. I honestly can't fathom leaving them in that situation when I had the ability to help - they are my parents.
I have worked hard to maintain a balance, but it still involves a lot of hard work from me. They get their day to day needs managed, but there is a lot more to it. We desperately need more geriatric care managers that help with all the details of their lives - there are none in their town. Stuff comes up. My plan for my next visit involves 3 drs. appointments and some banking, plus the normal tasks of helping mom sort through her junk mail, etc. I agree that you can't force siblings to help, but it sure would make it easier if we divided the workload and if those who live close enough would take on some of it.
In this case, the OP obviously has some work to do to make it more manageable, but even that will take work and time to accomplish. Not only will she need to let mom fail, but she'll probably need to help mom get things set up when she cries uncle. Her mom became needy very young and seems to be playing games since she is still "able" enough to work and drive, so it's hard for us to fathom, but the reality is most of us will get to a needy stage at some point. All of us hope to keep our faculties and be able to manage ourselves to the end, but that's simply not everyone's reality. Until you have experienced it, you have no idea how overwhelming it is. OP was venting out of frustration and her frustration is valid.
My DH's dad dropped dead out of the blue young. He was only 73. That was really hard, but after watching my parents my DH says now his dad went the easy way and he hopes he does the same.