Dagmar Overbye hailed from Denmark and worked as a nanny. All her victims were children. She even killed her own. Overbye was not merciful about it either. Many of her victims suffered tremendously, and she had multiple methods of torture and killing.
Blackpackerverse
Overbye did everything from strangling the children to drowning them. What she is perhaps best known for, however, is burning victims alive in her masonry burner. Reassuringly, Overbye was caught and forced to pay for her crimes. She was sentenced to death, one of three women to ever receive the death penalty in Denmark. That punishment was later dropped in favor of lifelong imprisonment.
26. Marybeth Tinning
Marybeth Tinning gave birth to nine children, all of whom died due to various causes. Although the age at which her children died varied, none of them lived to be any older than five. The first eight all died tragically, and all their deaths were regarded as just that: thoughtless tragedies.
Murderpedia
However, Tinning’s ninth child died under suspicious circumstances. It was ruled that her daughter, Tami Lynne, had been suffocated to death. This was the only death for which Tinning was charged, although it is widely debated if she had been responsible for the others. She was sentenced to 20 years to life in prison.