What Causes Black Worms In Urine Along With Abdominal Pain?

Hi Doctor. My daughter is 15 years old. she experienced abdominal pain and nausea yesterday all day. This morning at 2 a.m. she went to the bathroom and saw black worms. She has itching. I took her to the medical center and the doctor (general) is convinced that the worms can t be black (he has never seen such a thing and worms are always white). He might be right but I saw the worms in the bathroom and they were black. The urine test that we have done showed nothing. The lab technician advised us to consult an abdominal specialist/doctor. Also, she has constipation since a week. Can you please advise on the cause of this and how I should proceed.