Complex sentence: She visited the HQ of the SS almost daily to petition for her husband's release until 1940, when she finally, and incredibly, obtained permission for an audience with Heinrich Himmler and he secured Alfred's release from the Mauthausen concentration camp.
Split into simpler sentences: She visited the headquarters of the SS almost daily to petition for her husband's release. In 1940, she obtained permission for an audience with Heinrich Himmler, who secured Alfred's release from the Mauthausen concentration camp.