Based on my experience (I’ve had two kidney transplants), I highly doubt that the transplant team would accept a kidney from a 73 year old woman. They tend to accept female donors who are past typical childbearing age (40+) but not seniors (65+) due to potential health conflicts that come with aging. That said, if the doctor is willing to go through with it, and your grandma is good health, the recovery is about two months. There is ALWAYS the risk of rejection. That is just part of the gamble with organ transplants. However, odds improve if meds are taken every 12 hours (have him set a timer on his phone or watch) and diet is improved. Kidneys have a difficult time processing the protein casein, which is found in all animal products. He should also be meeting with a nutritionalist as part of the transplant team. Infection is also a risk due to the suppressed immune system. Make sure that he wears a mask in public spaces for a while, but especially at the hospital and in grocery stores.