A child whose status has been adjudicated by a juvenile court, or the child’s parent, guardian, custodian or spouse may, at any time within 15 days of the filing of the court’s order, petition the court for a rehearing on the grounds that new evidence has been discovered affecting the advisability of the court’s original adjudication or disposition. Upon a showing that such evidence does exist, the court shall order that a new hearing be held within 30 days, unless the court extends this time period for good cause shown within the 30-day period, and shall make such disposition of the case as the facts and the best interests of the child warrant.