What Causes Vomiting Up Of Blood During Third Trimester Of Pregnancy?

A young pregnant friend is with me. She is in the third trimester, stressed, alone and woke me at 3am concerned she threw up some blood. I asked her if she ate much today and she said yes. She does not seem to have a fever and her color looks ok. This is her second child and no complications other than placenta pre via which has moved. She is not on bed rest. I put her to bed and am monitoring her. She is a local college student and her family is over three hours away. The closest emergency room is an hour.