Both Princess Märtha Louise of Norway and her husband Ari Behn are authors. On which theme did Märtha Louise write a book?

Explanation

Princess Märtha Louise, the only daughter of King Harald V and Queen Sonja and the younger sister of Crown Prince Haakon, has studied physiotherapy, trained as a Rosen therapist and studied at an academy for holistic medicine. She claims she can communicate with animals and angels and has started her own alternative medical school named Astarte Education, named after one of the oldest goddesses in the Middle East.