My Daughter Has Been Very Sick. Nauseated, Vomiting, Diarreah, Not

My daughter has been very sick. Nauseated, vomiting, diarreah, not able to pee. We are currently in the emergency room. She has had one bag of fluids. I am concerned as why they are not giving her more fluids. A nurse told me they don't just give you fluids to make you pee. Should I be concerned?