My Daughter, Age 16, Says She Is Having Red Blood

My daughter, age 16, says she is having red blood discharge when she goes to the bathroom (bowel movement). Not always, but she says it has occurred several times and with more frequency. I tried to call the pediatrician last night but the doctor on call did not return call & office is closed. Could this be polyps ? Hemroyds? Something very serious? I plan to get her into dr as soon as possible but now am worried sick....she is at school