Complex sentence: In 1871 she became president of Evanston College for Ladies, which merged with Northwestern University in 1873, at which time she became the first Dean of Women of the Women's College.
Split into simpler sentences: In 1871 she became president of Evanston College for Ladies. That same year, the Evanston College for Ladies merged with Northwestern University and Willard became the first Dean of Women of the Women's College.