Hello sir I read your grandma history her age is 90 year having thyroid issue n also chf... Chf is more complicating factor if we give anaesthesia plus thyroid issue that would also additive complicating effect...in elderly person...having old age, chf,n thyroid issue none can stand with much stress that would be during long surgery...so we have short duration surgery only...now coming of facture femur than it should ve generally treated by open reduction n fixation by screw...as soon as possible....as femur neck has delicate arterial supply n very much chance of get necrosed if not treated earlier n once it get necrosed than we have to remove that part n put artificial femur neck...but it is also long procedure...n also much stressfull...n at last nothing can be done than last option is amputation...so may be in your case doctors n anaesthetic have only last option so they suggest this option