H.R.H - Danielle Steel

Princess Christianna, happier in jeans and a sweatshirt than in the formal life of European royalty, leaves university to travel to East Africa as a volunteer for the Red Cross. Determined to make a difference, she plunges into the dusty, bustling life of an international relief camp, and is anxious to keep her identity a secret from her fellow aid workers.
Dr. Parker Williams, who works alongside Christianna and shares her dedication to healing, has no idea who she is - but as violence approaches and invades the camp, and the pressures of her royal life beckon her home, her struggle for freedom takes an extraordinary turn.