If a person timely files, the person may apply to intervene in a proceeding before the Commission. The Commission shall grant leave to intervene unless the Commission concludes that: the parties to the proceeding adequately represent the interest of the person seeking to intervene; or the issues that the person seeks to raise are irrelevant or immaterial. An intervenor has all the rights of a party to a proceeding. In a proceeding before the Commission, an individual who is an intervenor may represent himself or herself.