Should old AGE affect decision of surgery???

My grandmother is 90 years old, and has just been diagnosed with Invasive Ductal Carcinoma, grade one. She is slightly "losing her mind", some days better than others. With the stress of surgery and the dangers of anesthesia, is surgery a definite "necessity"?  Or since she is so old already, would it be considered ethically "wrong" for the ones in the family that are her "power of attorney" and make medical decisions for her, to decide against surgery all together?  And let her just live the rest of her life without putting her through undue stress and physical dangers of surgery. Isn't the surgery itself, at that age, almost as much, if not MORE, a danger to her life than the grade one carcinoma??  Am I looking at this weird?  I guess I just don't want to see my frail, old grandmother, who gets stressed out about everything in daily life anyway, go "under the knife"! Are there alternatives like a major alkaline diet, etc. that would be acceptable for her age? Or is it JUST surgery, and that's IT, no question about it!... despite her old age? Thanks.