This isn't the first time a mother has murdered her children due to postpartum psychosis.

Maybe you should read up all about how Randy Yates abandoned Andrea and their children to the same fate because he simply couldn't stop pumping her full of babies.

Yates's first psychiatrist, Dr. Eileen Starbranch, testified that she urged her and Rusty not to have any more children, as it would "guarantee future psychotic depression." They conceived their fifth and final child approximately seven weeks after her discharge.[11] Yates stopped taking Haldol in March 2000 and gave birth to her daughter, Mary, eight months later on November 30, 2000.[12]

Yates seemed to be coping well until the death of her father on March 12, 2001. She then stopped taking medication, mutilated herself, read the Bible feverishly, and stopped feeding Mary.[9] She became so incapacitated that she required immediate hospitalization. On April 1, 2001, Yates came under the care of Dr. Mohammed Saeed; she was treated and released. On May 3, 2001, she degenerated back into a "near catatonic" state and filled the bathtub in the middle of the day; she would later confess to police that she had planned to drown the children that day but had decided against doing it then. Yates was hospitalized the next day after a scheduled doctor visit; her psychiatrist determined she was probably suicidal and assumed she had filled the tub to drown herself.[12][1]

At the time of the murders, the Yates family was living in the Houston suburb of Clear Lake City. Yates continued under Dr. Saeed's care until June 20, 2001, when Rusty left for work, leaving her alone to watch the children against Dr. Saeed's instructions to supervise her around the clock.[13] Rusty's mother, Dora Yates, had been scheduled to arrive an hour later to take over for Andrea. In the space of that hour, Andrea Yates drowned all five children.[14]

..

According to trial testimony in 2006, Dr. Saeed had advised Rusty Yates not to leave his wife unattended. However, Rusty began leaving her alone with the children in the weeks leading up to the drownings for short periods of time, apparently believing it would improve her independence, despite her doctors' instructions.[13] Rusty had announced at a family gathering the weekend before the drownings that he had decided to leave Yates home alone for an hour each morning and evening, so that she would not become totally dependent on him and his mother for her maternal responsibilities.[26]

I'm not even sure if I understand why you think punishing 1 woman is equivalent to punishing all women who commit violent crimes.