In addition to the above comments, it could be the food. My cat bleeds every once in a while, leaving blood spots behind. He's been doing this for as long as I remember. I even took him to the vet when he was 3 months old thinking maybe a cut, since kittens are so crazy and silly. The vet didn't find anything. Later, I realized my cat bleeds when he eats wet foods, no matter what type; premium, ultra premium, doesn't matter, the cat bleeds. Now I got to the conclusion that both wet and dry make him bleed, and so I'm trying to switch him to better nutrition.
What are you feeding her?
If they're very tiny dots of "blood", then this is probably flea "dirt". It looks like blood, don't know why it's called flea dirt, though!! Check your cat for fleas. If the kitten is old enough, you can use Advantage on her. That or Revolution, these are awesome. You've got to be sure she's old enough-there will be info on the pkg about age.
She's in heat. AKA her period!