How much longer will my mother with severe dementia live?

My mother, age 87, has had severe dementia for over five years. She does not know where she is or my name, although she recognizes me as someone close to her when she sees me. Her quality of life is nil. She has sundown syndrome and does not remember her childhood, her children, her grandchildren or great grandchildren. It is sad to see this once beautiful and vibrant woman live out her last years this way. We cannot care for her at home, as she is up all night and sitters were expensive and changed often. We only have enough money (with my help) for one year. Will she die from this or could she live 10 more years? I think somethings are worse than death.