What Causes Blood In Bowels Along With Nausea In A Child?

My 6 year old daughter just had a little blood in her feces for the first time ever. She had tiny nausea and tummy cramps on the bus ride home. All went away when she pooped. Her feces was small hard balls with the blood in it. I checked and whipped her after. No blood on rectum or hemeriods and she wiped clean. She has a history of constipation. Is this something I should worry about?