She actively campaigned for the rights of the women of Hawaii to vote prior to the passage of the Nineteenth Amendment to the United States Constitution in 1920.

Wilhelmine (nicknamed "Minnie"), whose name was sometimes spelled as "Wilhelmina", was born on March 28, 1861, at Lihue, Kauai, the daughter of German immigrant and businessman Hermann A. Widemann and his Hawaiian wife, Mary Kaumana Pilahiuilani.

Their wedding at the St. Andrew's Cathedral in Honolulu was attended by members of the Hawaiian Royal Family including King Kalākaua, Queen Kapiʻolani, Princesses Liliʻuokalani and Kaʻiulani.

[11][10][12] Carrie Chapman Catt, visiting from the mainland, was invited to speak with the group on October 28, 1918, and contributed to the growing interest.

One of the members said yesterday that up to the present time the native women have not known just what steps to take and therefore have made no progress but she said that with Mrs. Dowsett as the president they feel that the cause will surely advance.

[10]Wealthy women of Native Hawaiian and biracial descents like Dowsett, Emma Ahuena Davison Taylor and Emma Nāwahī were the initial leaders of this movement while women of Euro-American descent (i.e. the "missionary set") were less inclined to support the cause due to concern about the increased enfranchisement of non-white female voters.

On March 23, Dowsett and Louise MacMillan, a WESAH officer representing Hawaii Island, rallied nearly 500 women of "various nationalities, of all ages".

The following day, the House held a two-hour hearing on the issue of women suffrage and invited both supporters and opponents to speak.

[11][17] During World War I, Dowsett served as president of the Hawaiian Knitting Unit formed in March 1918 while her sister Emilie Widemann Macfarlane and her friend Emma Ahuena Taylor were to the first to organize knitting units on behalf of Native Hawaiian soldiers and servicemen abroad.