My parvo puppy had a seizure and bloody stool. What should I do?

I would notify your vet that she had a possible seizure first. Then I would try to make sure she has a consistent source of food or sugar to keep her glucose levels steady, in case that was the cause for her seizure. If you see the event happen again then it's best to record it so that your vet can see what is happening and classify the event correctly. Continue to give her fluids and other medicaitons as instructed by your veterinarian, unless possible seizure can be a side effect of one of her medicaitons (i.e. metronidazole).
If your puppy is a small or you breed dog then she is at risk for hypoglycemia (low blood sugar), so it's important to give her nutrical, Karo syrup or honey (1 tsp) every 4-6 hrs if she hasn't gained her appetite back yet. Once she starts to eat on her own then discuss with your vet how often she should get the sugar source, if at all. I hope that your pup survives her CPV infection. Best wishes and take care.