In 1910, Dennett's success in Massachusetts led the National American Woman Suffrage Association to aggressively recruit her for the position of Corresponding Secretary, reporting to Dr. Anna Howard Shaw. At the time, the NAWSA was ineffective and riven by factional conflict, which many blamed on Dr. Shaw's leadership. Taking the job required Mary to move from Boston to New York City, a hardship for her since she couldn't afford to move her children with her. Dennett successfully resolved much of the internal conflict in NAWSA within a few months, while supporting Dr. Shaw. Many prominent NAWSA members credited Dennett with reuniting the NAWSA membership and turning the organization around. In 1910, Washington State granted women the right to vote, the first state to do so in 14 years.