Daisy Louisa C. De Melker

Life Insurance poisoner, two husbands and a son.
She murdered the son because he was trying to 
blackmail her about the murder of the husbands.
Sentenced to die in South Africa, hanged in 1932.

http://www.angelfire.com/zine2/serialarchive/DEMELKER.html

http://www.geocities.com/Athens/Ithaca/7268/demelker.html

http://www.sundaytimes.co.za/1999/12/12/insight/in02.htm