Bien was born in the city of Fulda. She was married three times and was the heiress of her first two husbands, which later played an important part in accusations. In 1588, she married Blasius Bien and moved from the city, but returned after a conflict with her husband's employers.
At the time, prince abbot Balthasar von Dernbach, who had returned to power in 1602 after a long exile, ordered an investigation of witchcraft in the city. Over two hundred people were executed for witchcraft in witch trials that lasted until his death in 1605.
In March 1603, the investigations resulted in the first wave of arrests in the city. On 19 June, Merga was arrested and put in jail. Her husband protested before the Reichskammergericht in Speyer and pointed out that she was pregnant. In jail, she was forced to confess to the murder of her second husband and her children with him and one member of the family of her husband's employers, and that she had taken part in a sabbath of Satan. Her pregnancy was considered an aggravating circumstance; she and her husband had no children although they had been married for fourteen years. She was forced to confess that her current pregnancy was the result of intercourse with the Devil.
Bien was judged guilty of witchcraft and was burned alive at the stake in Fulda in the autumn of 1603.