Hello - HUMAWORM is not formulated to give a person diarrhea BUT diarrhea does occur in some people. One person might have 1 loose stool per day while another may never have any loose stools at all. Each person's body will react in different ways to getting rid of parasites and toxins. I am not trying to be vague but this really is how it works. She could wait until Christmas break if she thinks she will be prone to diarrhea. Thank you!