I have seen the progression of dementia up close and personal. It can be rapid or very slow. IF it is rapid she or any other Justice should have the integrity to retire and the same would apply to Presidents etc. Dementia is an awful disease, It would be cruel not to permit retirement.
I believe that she should stay as long as she can do the job because this is her profession and she obviously has a profound effect on our Justice system. Unless she has dire health problems, she shouldn't be badgered into retiring. This job is her calling and most people who have a calling need to feel purposeful in life.
For a Supreme Court justice, age and health don't seem to me to be relevant factors since the only relevant issue is her mind. She has to know the law and understand arguments presented to the court, and be able to evaluate them and present arguments in favor or against a given position regarding them. So age and health might be personal considerations for her, but not sufficient to expect her to retire. This question does make me wonder, though, what measures are in place to force retirement of a justice suffering from dementia which does affect mental capacity. Supreme Court justices are appointed for life, and I wonder if there might be political reasons for covering up a situation where a particular member is losing the ability to reason.
As a Justice of the Supreme Court, Ruth Bader Ginsburg has a lifetime appointment to her seat. Even though she has had health problems and lived through the death of her husband while still having her seat, and even though she is the eldest Justice, I don't feel that she needs to consider retirement unless and until she feels that she is no longer able to fulfill her obligations.
I think that Ruth Ginsburg takes her job very seriously and when she feels that she can no longer reliably make decisions at her highest capacity that she will willingly step down and retire, we have lifelong appointments and we should trust the individual to be able to make that choice.
I do not believe that Ruth Bader Ginsburg should consider retirement. I think that as long as she continues to do her job well and to expectations, she should be allowed to work. It also depends if she believes that she herself thinks she can do her job to the best of her abilities.