Your kitty needs to see a vet. There are so many things that can cause bloody poop or cat to bleed there. It may be her anal sacs are infected, it may be due to Irritable Bowel Disease (IBD) and food sensitivities. It may be due to an internal infection. The only one who can determine what the problem is is a vet, and the solution for each one is completely different, and a vet would know what to do.
You are right, it could be anything, I will do what the vet said and see what happens. She seems to be running around, eating, drinking lots, sleeping good, wet nose, and her butt looks clean, no sign of blood. I am thinking she ate a shell from the sunflower seed and it came out and cut her. I am also thinking because of how much she eats, it could also be worms.