In her work in India and Bhutan from 1955 to 1992, she served many Muslim women whose husbands and fathers would not allow them to be treated by male doctors.

When she returned to the United States in 1992, she moved to San Diego to serve HIV and AIDS patients because she believed the need was great.

Her dedication extended further through part-time volunteer work at St. Vincent de Paul Village-Joan Kroc Medical Clinic for individuals experiencing homelessness.

[4] During her first semester of college, she attended a speech by Mother Anna Maria Dengel, an MD who had founded the Medical Mission Sisters of Philadelphia (MMS) in 1925.

[15] Cumulatively, she spent nearly 40 years working in a variety of roles including surgeon, chief of surgery, and hospital superintendent, at Kurji Holy Family Hospital, Village of Mandar, Rachi District, State of Bihar, with four years (1960–64) in Patna, India, serving many Muslim women whose husbands and fathers would not allow them to be treated by male doctors.

[17] Its services included general care, surgery, obstetrics-gynecology, pediatrics, a pharmacy, a substance abuse detox center, and a nursing school, all of which she oversaw while serving as hospital superintendent (1987–1992).

While in India, she started a nonprofit charity, "Sr. Niedfield's Brothers", to collect funds for surgical instruments and medical supplies.

[8] On April 24, 1967, the work of the MMS was honored by Representative Joshua Eilberg (D-Pennsylvania) when he read a citation including her name into the Congressional Record.

[20] In the book The Hills Around Me, author Imtiaz Fiona Griffiths describes how Dr. Niedfield saved her husband's life in India by performing emergency surgery.

However, the Buddhist Bhutanese government was eager to update the quality of its healthcare, so health ministers invited her in a non-missionary capacity.

She dedicated one of these trips (1976–77) in service as a staff physician with the American Medical Association's "Project USA" program in support of the US Department of Health, Education, & Welfare.

[2] In those years she was also a part-time volunteer at the St. Vincent de Paul Village-Joan Kroc Medical Clinic in San Diego, serving people experiencing homelessness.

[25] In 2001, largely due to failing eyesight, she retired from practicing medicine at the age of 81 and moved to the Regina Residence in Orange, California, run by the Sisters of St.