Amanda was born in the 19th-century to a presumably wealthy background. According to Gambit her "roots" (family) were "greedy and encroaching into soil made of old money".  Under unspecified circumstances, she married a commoner husband. His first name "Daniel" and image were known to a time-traveling Gambit, though not his last name. 
In 1891, after surviving a series of miscarriages, Amanda Mueller was accused of being the Black Womb killer. Her obstetrician was none other than Dr. Nathan Milbury, an identity used by Mr Sinister. Mueller was married to Daniel Summers, who left Amanda with their only son because he couldn't handle the accusations.
Around World War II she was part of government research project that was gaining research on mutants. Other members included Kurt Marko (father of the Juggernaut and stepfather of Charles Xavier) and Irene Adler (lover of Mystique). Amanda must have had a slowed aging factor as she gave birth to a woman called Fontanelle who was in her early fifties in the early twentieth century.
Amanda headed the Black Womb Project in her later years. In one video she smothered a mutant child for her research.