When an airline denies boarding to a passenger by requiring additional travel documents to those requested by immigration authorities, that constitutes "denial of boarding" within the meaning of the Regulation. In case of denial of boarding the passenger has according to the Air Passenger Rights Regulation, a right to financial compensation (250, 400 or 600€ depending on the length of the flight) and assistance (reimbursement of the full cost of the ticket or rerouting to final destination on another flight).

I understand that in your case your partner could indeed take her flight as she also showed an identity card in addition to her passport. This being said I will contact the Norwegian National Enforcement Body responsible for ensuring the full compliance of airlines with their obligations under the Air Passenger Rights Regulation and ask it to enquire about this practice of Norwegian Airlines. National Enforcement Bodies can sanction airlines if they do not respect the Air Passenger Rights Regulation.