Platt studied at the Art Students League from 1929 to 1933 and at the New York Continuation School from 1933 to 1934. She won the Chaloner Prize in 1940, a grant from the American Academy of Arts and Letters in 1944, and a Guggenheim Fellowship in 1945.
She was a specialist in portrait sculpture and did a number of busts of members of the government, especially the judiciary. Her bust of Justice Louis D. Brandeis is at the Supreme Court Building in Washington; one of Justice Learned Hand is at the Harvard Law School Library; and those of Charles C. Burlingham and Harrison Tweed are at the New York Bar Association. Platt also executed a number of medallion portraits including those of Manley O. Hudson, James Ewing, and Junius Fishburn. She was a member of the National Sculpture Society.
