Perkins was a well-known quantity to FDR, agitating for labor reform and serving the state of New York in various capacities in the years before he was elected. But she almost didn't take the position.
"... Jane Addams and others campaigned for Perkins to be Secretary of Labor and urged ER to help secure the position for her," notes a short article about Perkins published by the Eleanor Roosevelt Papers Project of George Washington University. "Perkins, convinced that a person from organized labor should hold the post, initially refused and suggested a woman trade unionist instead. The pressure on her to accept the position increased, and after telling FDR that she expected the administration to side with liberal labor practices and that she wanted to spend weekends in New York with her family, she accepted the position. Labor objected, arguing that she had no experience with unions and little ties with the labor movement, but she defused their opposition by downplaying her position and praising the role of AFL president William Green.
"As a key labor advisor to FDR, she helped shape the Civilian Conservation Corps, the Federal Emergency Relief Administration, the National Labor Relations Act, the Social Security Act and the Fair Labor Standards Act. She also shepherded the United States' entry into the International Labor Organization, and remained its active supporter throughout her life. She resigned July 1, 1945 so that Truman could appoint Lew Schwellenbach..."
She died in 1965. The GWU biographical sketch is here.