P.M.
That's one of the varied, joyful ways a digestive virus (sometimes called stomach flu) can make itself known. If that's what she has, then she should be better within the next 24-48 hours. If she seems to take a turn for the worse, develops a significant fever, or is completely unable to eat or drink, then call your doctor's office for advice and maybe an appointment.
If it does not begin to improve within two days, there are other potential problems, such as an intestinal blockage or appendicitis (nausea and dry heaves were the only symptom I had for the four days before my appendix burst). I would definitely call the doctor if she stays ill.
Poor little kid – nausea is no fun, and can be very exhausting. Try to keep her sipping water or pedialite. I hope she feels better soon.