She competed in the 1928 Summer Olympics in Amsterdam and in 1932 in Los Angeles, winning a gold medal in the 100 m backstroke and a silver in the 400 m freestyle in 1928.

She failed to reach the finals of these events at the 1932 Games due to a sudden illness during the preliminary heats.

She had her first international success at the 1927 European Championships, where she won one gold and two bronze medals in the 100 m and 4 × 100 m freestyle and 100 m backstroke.

[1] During the 1932 Olympic swimming competition in Los Angeles, Braun suddenly became very ill and was hospitalized for three weeks with a high fever.

[3][4] When she returned to Nederlands, she gave a press statement stating that between events, she suddenly felt a pain in her leg and that two young American men who had been sitting in front of her in the stands and had been watching her suspiciously, "disappeared".