The department shall not consider the disability of a person to be the sole factor in making a determination under section 346-17 or section 346-19.7. If the department makes a determination to deny the petition of a disabled person under section 346-17 or section 346-19.7, the department shall make specific written findings stating the basis for the determination. The party attempting to demonstrate that the disability impairs a person’s ability to parent must prove that the disability is a factor, and demonstrate a clear nexus between the disability and the alleged parental deficiency.