Blood in urine

My 5 year old has been having bad stomach issues and she vomited today and she also has been complaining of back pain. They found blood in her urine at ER and I’m very scared they said to follow up with urologist. But what can it be from? She did have UTI recently.

Edit they did a ultrasound and urine test & X-rays they said X-rays or ultrasound didn’t show anything they said she don’t have infection anymore but blood in urine that they don’t know why but follow up with urologist