She was president of the Women's Overseas Service League from 1933 to 1935, and was state regent of the Daughters of the American Revolution for the District of Columbia in the 1950s.

[3] Dennis served for sixteen months with the American Red Cross in France and Germany during and after World War I.

[8] She worked for women's access to services including veterans' hospitals and care homes.

[9][10] In related work, she was a unit president and national defense committee chair of the District of Columbia's American Legion Auxiliary.

[11][12] During World War II, Dennis was a leader of the casualty shock-feeding teams of the Red Cross Canteen Corps in the District of Columbia, volunteers trained to organize emergency services such as food relief and first aid stations, in a disaster or attack.