What Causes Gallbladder Stones After Following HCG Diet?

My daughter lost 100 lbs on the HCG diet. Took her 5.5 mos and has been doing phase 3, the workouts for about 3 mos. today she suffered a gallbladder attack and had to have emergency surgery. She had hundreds of stones that she will need another surgery tomorrow to remove the stones through her mouth. Have you any insight in these HCG drops and the restricted 500 calorie a day diet relating to gall bladder issues? Now I m googling all kinds of warnings about these drops from the FDA, AND THAT THEY ARE ILLEGAL, TRUE?