I found more on Elfi Kreigs-Au Carroll-largely thanks to Jimbo's research.
KRIEGS-AU, “ELFI” (Elfriede Kriegs-Au)
Born 05 November 1915 in Vienna, Austria
Died 01 March 2004
Married Ronald Carroll (born circa 1913) by 1940 census, possibly as early as 1935
Active in local New York tennis up to 1969.
Came to the US circa 1939. 1940 census (which lists her as Elfe) shows she had lived in Havana, Cuba in 1935, had 4 years of college, and was living Queen’s, New York city, New York. Her spouse Ronald was born in Poland, and like Elfi in 1940 was not yet a citizen. Ronald was also in Havana in 1935, so they were probably wed by that date.
First mention playing tennis in the US in the NYT in June of 1940.
She was ranked No. 14 in the United States by the U.S. Tennis Association in 1952. She was a member of the U.S. Paddle Tennis Hall of Fame. She was an avid bridge player and a sailor. Survivors include two sons, Michael A. "Mike" Carroll, Greenlawn, N.Y., and Thomas G. "Tom" Carroll, Tinton Falls, N.J.; a sister, Maidie Kriegs-Au, and a brother, Dieter Kriegs-Au, both of Vienna;
Her obituary is in the St Petersburg Times. Last residence: 33703 Saint Petersburg, Pinellas, Florida.
Won 1949-1952 Women’s Eastern Clay Chmps (of New York?) Played Forest Hills in 1951. She used a western grip forehand to produce good topspin.
• In platform tennis HOF (1970). Women's National Champion 1950, 1955 and 1958; finalist 1951, 1952,1953, 1957 and 1960.
• National Mixed Doubles Champion (with her husband) for four straight years - 1949, 1950, 1951 and 1952; finalist 1953 and 1958.
Link with a picture: