Shane, I think it's wonderful you are trying to help your little sister. Loss of weight and stomach aches are definite signs of parasites. For me, those were the two biggest indications. If all this started after her trip to Cambodia, than I would be even more concerned that she could have parasites.
I would go with the ParaGone for kids, as Susie recommended. And for you, the adult ParaGONE. Check at your local healthfood store or you can buy them both online -