For seven years, Luo Hongmei toiled in factories in China’s southern Guangdong province, experiencing firsthand the daily struggles that face millions of young female workers before deciding to join China’s fledgling labor-rights movement. As director of the Guangdong-based nonprofit Sunflower Women Workers Center, her mission is to bring attention to—and, she hopes, find solutions for—women’s workplace issues, such as unpaid maternity benefits and illegal firings for becoming pregnant. Recently Luo oversaw a study about another disturbingly common and little-discussed problem: rampant sexual harassment...