"Streams to the River, River to the Sea" by Scott O'Dell

I loved this book as a teen.  I loved this book again now.
Streams to the River, River to the Sea is a fictionalized account of Sacagawea's life.  It begins with a fictional description of her life beginning as a pre-teen when she is captured by an enemy tribe and literally groomed to become the chief's son's wife.  A half-French trapper named Touissaint Charboneau wins her in a gambling game and decides to make her his second wife.  Shortly before she gives birth to their first child, the Lewis ...