Other than eGFR (function), sysmptms of kidney failure also play a role to decide when dialysis needed. Plz talk to a nephrologist.
Most patients continue to decline and require dialysis for survival. A patient needs to be prepared to do dialysis when the time comes and preparation takes time. Prepared patients do better in terms of quality of life and survival; that is the reason to discuss and prepare for dialysis
Usually, dialysis may not be needed at a GFR of 20, but that is the time an access is planned to ensure that patient can start dialysis in future. Some patients with issues with volume management or persistent hyperkalemia may need to start dialysis at GFR more than 15, but not too many. If she has multiple comorbidities and does not want to do dialysis, then there are options for medical management with dietary modification and supplemental medications. It is difficult to say what the long term prognosis or duration of life may be for each individual patient without actually evaluating them. Data shows that elderly, debilitated patients with multiple comorbidities may not do as well on dialysis as those without these risk factors. Please feel free to come for a second opinion, if you would like to.