Well, according to King Harald, The Royal Court and several Norwegian authors, she died of these reasons:
From 1946 to her death in 1954, she suffered from various illnesses, such as, sciatica and jaundice. During this period, she was frequently hospitalized, and spent some recuperative time in Florida. She had several remissions, but never fully recovered from it. After another attack in early March 1954, she was again hospitalized. - And on March 21th, the family celebrated the CP couple’s silver wedding anniversary at the hospital.
She died quietly on April 5th at the Rikshospitalet, surrounded by her husband CP Olav, her father-in-law King Haakon VII, her children, her sister Princess Margaretha, and her brother-in-law Prince Axel. Her brother Prince Carl Bernadotte was delayed by the weather.
The cause of death was (according to King Harald and The Royal Court) hepatitis, and the infection had occurred after a Blood transfusion - in connection with an operation in the United States during the war years.
Her death led to an outpouring of public grief.
Norwegians are girls who love girls, boys who love boys, and girls and boys who love each other. King Harald V speaking in 2016.