Complex sentence: Lost Woman's younger sister, Washakie's aunt was Nanawu (Little Striped Squirrel), the mother of Chochoco (Has No Horse), who was therefore a first cousin to Washakie.
Split into simpler sentences: Lost Woman's younger sister, Washakie's aunt, was Nanawu (Little Striped Squirrel). She was the mother of Chochoco (Has No Horse), a first cousin to Washakie.