Mama, I know this is scary, but please don't wait, bring her to the ER or call your pedia now before the scheduled appointment, especially with bloody stools and sudden changes like that. Blood in poop always needs to be checked right away, kahit active pa siya.
I can't guess what it is, but a doctor needs to see her today to rule out what's happening. Better safe than sorry, diba? Praying she's okay!