What Causes Yellow Drainage From Anus In A Child?

Hi my daughter is 10yrs old has just ended her periods and has noticed a bright yellow discharge from her anus. She has a bad habit of holding on going to the toilet and does inturned have large stools. She passed one only 3 days ago. She has no ongoing pain, no no blood when she wipes and has no itching. We are going to the gp tomorrow but im a worried mum and was hoping you would be able to guide me as to what this could possibly be?