Sister Mary Reginald Gerdes, a former Saint Frances Academy principal who broadly expanded the school’s enrollment and made it coeducational, died of heart failure Sept. 7 at her order’s motherhouse in Arbutus. She was 88.

“She transitioned St. Frances from a select, female academy to a coed powerhouse,” said the Rev. Michael Roach, pastor of St. Bartholomew’s Church in Manchester. “She was an extraordinary person, a fine teacher and historian. She was the expert on French-speaking people of color in Baltimore in the 19th century. She was also an activist in the civil rights movement when she served in Charleston.”

Born in New Orleans, she was the daughter of Louis Gerdes, a roofer, and his wife, Almira. She was the oldest of six siblings.

In a 1992 Sun article, she recalled Christmas Eve in her childhood: “Around 10 at night, my father would come in. On that night, he might let us have a little bourbon and Coca-Cola. But only on that night [but] we girls were never allowed at midnight Mass.”

In 1952 she joined the Oblate Sisters of Providence, a Roman Catholic religious order of which a cousin, Sister Mary Martin, had been a member.

“She was very proud of her New Orleans roots and the Creole culture,” Father Roach said.

Sister Reginald earned a bachelor’s degree at Marillac College and a master’s degree at Duke University.

She taught at Our Lady of Divine Shepherd School in Trenton, New Jersey, Holy Name of Mary in Chicago; Saint Frances Home in Normandy, Missouri; and at Bishop England High School in Charleston, South Carolina.

She began teaching mathematics and biology at St. Frances Academy on East Chase Street in the Johnston Square neighborhood in the 1970s. She became the school’s principal and worked to transform it from an all-girls institution to a coeducational institution. She built up a network of benefactors, including parking garage owner Allen I. Quille, and raised funds to get a gymnasium built.

“She was a larger-than-life person,” said Ralph Moore, the chair of By Peaceful Means. “She wasn’t afraid to face down neighborhood toughs. She wasn’t afraid to face down elected officials.”

He recalled the rapport she established with Mayor William Donald Schaefer.

“Schaefer would come and have a breakfast with Sister Reginald and the other sisters,” Moore said. “I recall one day they were talking about the sisters living in rowhouses on Brentwood Avenue and how they had taken out a city loan to renovate them. Schaefer said to a housing aide there, ‘Make that loan into a grant.’ “

“I held a heart of admiration for Sister Reginald,” a former student, Therese Wilson Favors, said in a 2012 Catholic Review article. “She was no one whom you would want to be on the wrong side of. She disciplined with her words, and let’s not forget her body language, which could correct ... in just one glance. Sister Reginald ... is fiercely honest and positively challenging.”

After she had stepped down as principal, she continued to reside in Johnston Square. In a 1987 Sun article, she described how she welcomed children, carrying their homework, coming through a chapel door.

“Soon, a nun appears and the reading lessons, arithmetic tutorial program and supervised play begin,” the article said. “The Oblate Sisters of Providence cannot say no to any child who wants to learn. Their gift to their neighborhood is this informal after-school tutorial program that also provides a haven for children of crime-ridden, impoverished Johnston Square, a section of East Baltimore that stretches south of Green Mount Cemetery to the city jail.

“The children like to come to wherever the sisters are,” the article said. “‘They like to learn. This group, in particular, is good. We have one little girl who wants to do nothing but math,’ said Sister Reginald Gerdes. ‘We let the older boys address the smaller children from the neighborhood. They can get to them better than I can. We want the older students in the academy, the high schoolers, to be role models for the younger children. We teach responsibility.’”

Sister Reginald said she had watched the neighborhood grow less stable.

“I’ve watched this part of the city change. The children don’t seem to have any supervision. They want love, attention. They flock to our door. We can’t turn them away.”

Sister Reginald also said in 1987, “My real dream is to create an endowment fund so that any child in Baltimore could come to St. Frances and receive our education.”

Sister Reginald later lived at her order’s Baltimore County motherhouse and became the archivist. In 2004 she helped display samplers made in the 1830s by the students at what was then called the School for Colored Girls of the Oblate Sisters of Providence. She told a reporter her order preserved 15 rare samplers made by students in the 1830s and 1840s.

In her retirement she wrote numerous letters and worked to endorse the cause of sainthood for Mother Mary Lange, the founder of the Oblate Sisters.

A private funeral Mass is being offered Tuesday.

Survivors include her brother, Louis Gerdes Jr. of New Orleans, and three sisters, Iris Billinger of Long Beach, California, Barbara Moore of Aurora, Ohio, and Joyce Joseph of New Orleans.