Red Lawhern
Unless your sister happens to be living in the UK or Canada, I can think of no earthly reason why she or anybody else should have to wait for gallstone surgery for 15 months. If she already has gallstones forming, they will show on high resolution imagery (MRI). As far as I know, there's no dietary approach that can reduce them once they start forming. A nutritionist may be able to provide advice concerning diet to reduce the rate of growth. Having had my own gallbladder removed after an attack of gallstones, I would personally consider getting another doctor or emigrating to a country whose medicine is not socialized, if I were told to wait that long after diagnosis of stones. That is simply malpractice, by any measure.