Kitty has a little blood in litter box?

If she were my kitten I'd have her looked at by a vet. Take a poop sample to be checked for parasites. Collect a sample and keep it in the fridge until you can get it to your vet...no longer than 24 hours. Make sure you're feeding a food that you didn't buy from a grocery store. Those foods have inferior ingredients, like corn and by- products, and will not keep your kitten healthy throughout it's life. Try a food such as Blue Buffalo or Wellness. They are Quality brands that have the protein, from real meat, your kitten needs to live a long, healthy life.

You should have her checked by the vet but it is not an emergency unless you see lots of blood or if she is in a lot of distress. I would call the vet on Monday get an appointment and bring a stool sample with you. They will send the stool out to the lab or test it in house for parasites. Not all intestinal parasites can be seen a lot of parasites are microscopic. Round worms, Giardia, and coccidia are the most common parasites/ protazones in kittens. There are other types of intestinal parasites as well. If she should come up positive for any they are all treatable with oral medication. What you are seeing is what you call frank blood meaning fresh blood streaked on or near the stool which can be a result of straining or parasites.

Have you wormed your kitten yet? If not, go get a dewormer and give it to her and she will be better in a couple of days. You may not see the worms in her poop, might be in her tummy. If you have already dewormed her, then get her to the vet and take a stool sample with you and they should let you know what is wrong with the kitty pretty fast.

From human to animal blood in stool requires vet or doctor ASAP!

I would still take her to the vet could she be in heat?

Maybe her poop is to hard and it makes her butt bleed