what color is the blood, the clear red indicates blood near the end of rectus, and dark red indicated almost from stomach.and also smell putrid smell(blood smell, i know poop smells but with blood involved it smell different)indicates serious intestinal disease.
and if it really just a spot it could be that it got scratched, even from feces, but just to be unworried get her checked, it does no harm and gives you peace of mind.