[4] In 1938, Thea, her Polish husband Kalman Schlachet and their son Peter came to the United States as Jewish refugees from Nazi Germany,[5][6] and she eventually gained American citizenship in 1944, at which time she took the surname Tewi.

[4][7] Tewi continued studying throughout her life, attending the SculptureCenter between 1953 and 1956, the Art Students League from 1954 to 1955, and in 1955, alongside Seymour Lipton and Manolo Pascual, she went to The New School for Social Research.

[8] Reporting on fashion trends that year, the Detroit Free Press referred to Tewi's "naughty-nice lingerie" featuring "daring cuts" and racy appliqués.

"[10][11] In 1947, the Textile Colorist journal, while reporting on Tewi's electric-blanket inspired nightgowns, noted that she had been named America's top lingerie designer.

[5] Her stonework included an art deco style headstone for the grave of Frederick and Helen Serger in Maple Grove Cemetery, Queens, New York.

[4] Her work is also owned by The Bank of Tokyo, Citicorp, the New York City Department of Parks and Recreation, and Pfizer.