Early years In 1927, she joined the local tennis and hockey club. From 1928 to 1930, Horn took part at the German junior championships where she lost to Edith Sander twice in the finals. Horn participated at
Wimbledon from 1932 to 1937, reaching the quarterfinals in singles in 1936. She was the top player on the German national ranking in 1936 and 1937. In 1932 and 1937, she was ranked world No. 8 by British journalist
A. Wallis Myers. In 1937, Horn went on a world tour together with the best German male players
Gottfried von Cramm,
Henner Henkel and coach
Heinrich Kleinschroth which led them to the United States and Japan. In Japan, she won the national mixed-doubles title with
Ryuki Miki. At the
1937 U.S. Championships, she reached the third round in singles where she lost to
Dorothy Bundy. In doubles, she teamed with
Anita Lizana; they were defeated in the quarterfinals by
Sarah Palfrey and
Alice Marble. In mixed doubles, she played with von Cramm and also reached the quarterfinals. After their stay at Japan, the men continued their trip towards Australia, and Horn returned to Germany from Manila. ==Grand Slam finals==