smelly stool in child

My daughter is 18 months old. She is on a vegan diet: fresh fruits, veggies, beans, nut butters, and whole grains. She doesn't eat any junk. I don't know why, but her stool smell is horrible lately. It use to not have any foul smell at all. It smells like poop smells when it's been fermenting inside your colon. It's sour smelling. It is like this every time she goes, and she goes from 3 to 6 times a day. Does anyone know what could be wrong? Tweet