Except in the case of a medical emergency or except as provided in sections 71-6902.01, 71-6903, and 71-6906, no person shall perform an abortion upon a pregnant woman unless, in the case of a woman who is less than eighteen years of age, he or she first obtains the notarized written consent of both the pregnant woman and one of her parents or a legal guardian or, in the case of a woman for whom a guardian has been appointed pursuant to sections 30-2617 to 30-2629, he or she first obtains the notarized written consent of her guardian. In deciding whether to grant such consent, a pregnant woman’s parent or guardian shall consider only his or her child’s or ward’s best interest.