Louisa May Merrifield, originally named Louisa May Highway, was born on December 3, 1906, in Wigan, Lancashire. She was the youngest child in her family, with five surviving sisters and two brothers. Her father, Job Highway, worked as an underground laborer in a coal mine, and her mother was Emma Duncan.

Louisa married Joseph Ellison in 1931. Together, they had six children, but only four survived past infancy. Tragically, two of their children, Horace Ellison and Ernest Ellison, died when they were very young. In 1946, Louisa was convicted of ration book fraud and served an 84-day prison sentence. Because of this, she lost custody of her four surviving children.

Joseph Ellison passed away in 1949 due to sub-acute infective hepatitis at the age of 44. Shortly after, Louisa married Richard Weston, who was 78 years old. This marriage lasted only ten weeks, as Weston died from a heart attack soon after they wed.

On August 22, 1950, Louisa married again, this time to Alfred Edward Merrifield, a 68-year-old widower. Alfred had previously abandoned his first wife and their ten children in 1928. From 1950 until the time of her later crimes, Louisa held around 20 different jobs as a domestic helper and housekeeper. However, she was often fired or had to leave due to her poor work habits and accusations of theft.

In March 1953, Louisa and Alfred took jobs as live-in companions for a 79-year-old widow named Sarah Ann Ricketts. Ricketts lived alone in a bungalow in Blackpool. Despite being small in stature, she was known to be difficult and had a quick temper. Soon after the Merrifields began working for her, Ricketts complained about their lack of care and their spending habits.

In 1953, she was hired to look after 79-year-old Sarah Ann Ricketts in her home in Blackpool. After a short time, Louisa started to make odd comments about Ricketts and her potential death. On April 12, Louisa told a friend she had to return home to "lay out" an old woman, implying that Ricketts would soon die.

On April 14, Ricketts died, but Louisa did not inform anyone until the next day. During that time, she made arrangements for a quick cremation and requested that the Salvation Army band play music outside her home. She expressed a desire to keep Ricketts' death a secret from the woman's family.

When authorities learned of Ricketts' death, they conducted an investigation that revealed she had died from phosphorus poisoning, linked to a rodenticide that Louisa had recently purchased. Records showed that she had signed for the poison, and the police were alerted after Louisa's friend reported their earlier conversation about Ricketts.

Louisa and her husband, Alfred Merrifield, were arrested and charged with murder. They faced a trial in July 1953, during which several witnesses spoke against Louisa. Her friends recalled her boasting about an inheritance from Ricketts, and one witness mentioned that Louisa had spoken of poisoning Ricketts if things continued as they were.

Despite a defense seeking to argue that Ricketts did not die from poisoning, the jury found Louisa guilty of murder after just six hours of deliberation. The judge described her actions as particularly cruel. Alfred was unable to be convicted, and he was later released.

During the following weeks, Louisa was sentenced to death by hanging. She appealed the verdict, but her appeal was dismissed. Despite efforts from others to save her, she was executed on September 18, 1953, by hanging at Strangeways Prison in Manchester. Louisa was the fourth and last woman executed there and one of the last women hanged in the UK. Her body was buried in an unmarked grave alongside other executed prisoners. After her execution, Alfred continued to live at their bungalow and later gained attention for being the husband of a convicted murderer.