Hellogirl1 Some times you have to be cruel to be kind. You need to sit and talk to your daughter and tell her that you are reaching a point in your life where looking after her is too physically demanding and you may not be able to do so for much longer.
Could you seek some councilling to help you approach this subject with her? Could you speak to Social Services, who, I presume, are aready involved through organising and providing her care, about the situation, and what care she would get when you were not there through infirmity or death.
It may be that someone from Social Services or your local Carers UK, or Age UK can talk to your daughter. She needs to realise that not talking about the future does not make it go away and only makes her situation worse when it does happen.
I have every sympathy for both of you, she must be so frustrated that her life has been so limited by this illness and, as a mother, dealing with an adult child with this illness, must be devastating.
I understand how your other children feel, this daughter's life must dominate yours, almost to the exclusion of them, but telling her not to be selfish, isn't helpful. But she does need to realise that life cannot continue as it is now, and the moment of change has arrived, whether she wants to speak or think of it of it, or not. But, as Social Services will undoubtedly need to be involved in any change, perhaps talk to them first.