Mary Ann Cotton - Just A Spoonful of Arsenic Helps the Medicine Go Down

Mary Ann Cotton was no Mary Poppins!  She is often referred to as the first female serial killer of Britain in the 19th century, poisoning 23 people, including 11 of her children, 6 stepchildren, 3 husband's, her lover, her friend and her mother!   

References:
https://www.grunge.com/321450/the-messed-up-truth-about-19th-century-murderess-mary-ann-cotton/

https://en.wikipedia.org/wiki/Mary_Ann_Cotton

https://allthatsinteresting.com/mary-ann-cotton