Why did Julie in Julie of the Wolves have to get married to Daniel?

In the book julie marries daniel because before she had to leave her father kapugen to go to school and live at her aunt martha's house he said that she could escape martha if things ever got bad and go live with his "serious partner",Naka, his wife Nusan, and (if she chose to) her new husband Daniel. So when Julie can't afford to go to highschool on the mainland she has to stay home with Naka who soon becomes very cruel towards her and refuses to let her spend time with her friend judith who in her opinion is a bad influence. So when the indian bureau of affairs representative comes to send for julie she jumps on the chance to leave to barrow despite her aunt's wish for her to stay.