A little blood after delivery is normal for up to 8 to 10 days afterwards. However, that now being said, if you aren't 100% certain the placenta was expelled, then perhaps a call to the vet would be in order. He/She can instruct you on what you should do or if he/she wants to see your girl.
Blood is one of those things ... even a small amount of it looks like a lot. You should be seeing a small drop or two, and it should look and smell like blood. If it looks or smells like anything else, then call the vet. You don't want an infection to start blossoming in the uterus. Green or yellowish-green discharge is bad. But blood, as I said, a small drop or two every now and then is fine unless it continues for more than 10 days.
With newborn kittens, taking the momcat to the vet can be problematic. She can pick up things at the vet's office and bring them home to her kittens. It isn't common, but it happens. If you can avoid taking her to the vet, that would be best right now. The kittens need her to stay with them as much as possible for 1) feeding, 2) warmth and 3) comfort. They cannot regulate their own body temperatures at this early stage and taking the Mom away for even a short amount of time isn't recommended. Good luck.