KatyjI think a bit of tough love comes in here. Speak to your mother and tell her how much help you can give. Tell her, for example, that you will call in most evenings and do a weekly shop but cannot help with getting up, going to bed, cooking, cleaning or bathing - and then stick to it.
Speak also to social services and make it absolutely clear to them, that you are the only family she has and that you cannot offer the help she needs. They are used to elderly people telling them they need no help, that family can cope, but hearing from you - and you sticking to the limit you have said you can manage - will help bring it home to them.
It may mean a day or two when your mother has to spend a day in her night dress, and live on bread and butter. But the quicker everyone, especially her, realises that she has to accept outside help, the better.
It will not be easy, and in very different circumstances, I have had to refuse to give help I could not sustain to a dear one who needed it, and it was not easy, but had to be done. The result in the end was one that was better for all of us.
You have my sympathy at this very difficult time.