She was the president of the New Mexico Association of Indians Affairs for more than 20 years and helped found and was the trustee for several organizations that advocated for Native Americans.

She reported in the November 1920 Alumnae Quarterly that she "was one of the Suffrage Emergency Corps to visit Connecticut in May," alluding to the unsuccessful campaign to get the state to ratify the 19th Amendment.

[2] Dietrich moved to Santa Fe, New Mexico in 1927 with her sister, Dorothy Stewart, an artist,[12][13] and in 1928 bought the Juan Jose Prada House on Canyon Road,[14][15] which had been restored by Kate Chapman.

[16] She also restored the 24-room adobe hacienda of James L. Johnson, a trader on the Santa Fe Trail, called El Zaguán house.

[17] Dietrich continued her advocacy work in New Mexico for the Puebloan and Navajo people by lobbying against development of dams and exploration in villages.

[18] She raised funds for the New Mexico Association of Indians Affairs and developed programs to help Native Americans in the state.

[19] Through careful study she [Margretta Dietrich] has made herself familiar with Pueblo and Navajo Indians and their interests and problems.

[20] She was a patron for Native American art students of Dorothy Dunn (at the Santa Fe Indian School).

[21] Of a proposed dam site on Native American lands, she wrote: You also know that if these dams are constructed they will destroy several ancient Indian villages and flood their fertile lands which the ancestors of these present Indians were cultivating and irrigating even before the Spaniards came into this region in 1540... We believe it is your duty to inform the Congress that even to drill on Pueblo land may be desecration to their sacred areas and could destroy an important part of the only indigenous culture in the United States.Dietrich published three books in her lifetime and one was published posthumously.