You should consult with your pediatrician and see if a referral to a gastroenterologist (dr. who deals w/ the digestive system) is in order. As always, if she's having emergent severe symptoms, contact the on-call pediatrician or proceed to the nearest emergency room.
I am sorry that your daughter is still feeling bad. :( I would take her back to the doctor and request not only another xray, but an abdominal ultrasound to see if the marble has passed or if there is some other problem causing her tummy troubles. Sometimes xrays alone just don't pick up on things that are in the digestive tract. I hope she gets to feeling better soon!
I would take her back to get checked by the doctor again.
Either they missed the marble in the xrays or she now has a tummy bug.
As a marble is round and smooth it should have come out when she opened her bowels. How did she manage to swallow a marble?
When my daughter was 9 and had a lot of tummy problems, it turned out she had a lot of threadworms. She used to suck her thumb a lot.