The children's court, under any proceeding authorized by this part, shall appoint, for the purposes of the proceeding, a guardian ad litem for a minor, where the court finds that the minor does not have a natural or adoptive parent, guardian or custodian willing and able to exercise effective guardianship, or where the parent, guardian, or custodian has been accused of abusing or neglecting the minor.
25 C.F.R. § 11.904