She was born Marie Alexandrine Petitjean at Waasmont, near Landen, on July 14, 1879. She married Charles Becker, a cabinetmaker, and lived quietly in Liege for two decades. In 1932, in her fifties, she began an affair with Lambert Beyer, a man she met while shopping, and poisoned her husband with digitalis, a foxglove extract used in small doses to strengthen the heart. She then poisoned Beyer in the same way. He was her lover, not her second husband, as some accounts have it.
With money from Beyer's estate she opened a dress shop. Between 1933 and 1936 she poisoned elderly women who were customers of it, taking cash, jewellery and clothes from their homes afterwards. She attended their funerals and made a show of her grief.
She was arrested on October 16, 1936, after telling a friend who wanted rid of her own husband that she could supply a powder that left no trace. The friend went to the police. A search of her house turned up victims' property and a bottle of digitalis, and exhumations found the poison in the bodies.
Her trial at Liege opened on July 7, 1938, nearly two years after her arrest. She was convicted of eleven murders and five attempted murders, plus theft and forgery, and sentenced to death; the sentence was commuted as a matter of course, Belgium having last executed a civilian in 1863. She died in Forest prison in Brussels on June 11, 1942, under German occupation.
The remarks attributed to her at trial, including the line about a victim looking like an angel choked with sauerkraut, come from mid-century popular crime writing rather than from any court record, and are repeated everywhere without a source. They are noted here as attributed, not quoted as evidence.