Internal bleeding among other things. Take her to the hospital! Seriously I can think of nothing good that could mean.
It means call the doctor..
is she bleeding a lot from the mouth? then Id advise you to take her to the emergency room, immediately
If there is no obvious source of the blood in her mouth (no cuts or such), then I would suggest that she go to the doctor. Especially if she is throwing up blood, which could be from a complication to her surgery. She should also be checking for bloody or unusually dark stool when she goes to the bathroom. If she is bleeding from the surgery into her digestive system, more than likely it would be noticed there too.