Each and every surgeon and hospital will have different pre OP preparation So My suggestion is to decide the doctor and hospital first And Follow their regimen

After assessment the doctors might have rightly opined that your mother needs replacement. But she can make the replacement more successful by doing pre operative physiotherapy. During those sessions we would strengthen the appropriate muscles, teach her what she will be supposed to do after surgery etc. That will help her to face the surgery more confidently. Moreover for badly worn out joints replacement would be the best when preceded with quality pre and post operative physiotherapy.