Snakes' teeth are like razor blades... I've had bites that I can't even SEE bleed all over my hand. If the mouse had any blood on it, I bet that's where the blood on the paper came from.

Keep an eye on her, but I doubt there's a problem. Plus, if there was enough blood on the inside of her mouth to leave streaks on the paper, you'd be able to see where it had come out of the mouth.