Fellow board members and company executives, who have not spoken publicly about her role at Wal-Mart, say Mrs. Clinton used her position to champion personal causes, like the need for more women in management and a comprehensive environmental program, despite being Wal-Mart’s only female director, the youngest and arguably the least experienced in business. On other topics, like Wal-Mart’s vehement anti-unionism, for example, she was largely silent, they said.