Audrey Marie Hilley

Arsenic, three family members, possibly others, no known motive.
Arsenic in coffee, gave it to neighborhood children.  Poisoned 
her husband, her daughter, her mother-in-law, neighborhood children, 
and several cops.

http://www.crimelibrary.com/serial7/hilley/

http://www.familyofmen.com/female_serial_killers.htm
Book: "Black Widow: The True Story of the Hilley Poisonings"

http://www.newhorizonpressbooks.com/ts_crime/blackwidow.html

Book by Philip Ginsburg:
"Poisoned Blood"
Scribner's/Warner (January 1988)
Audrey Marie Hilley got away with murder. Then she almost got away 
with suicide. A pretty woman who appeared to be an ordinary homemaker, 
wife, and mother, a reliable worker who made friends easily, 
Marie Hilley has been called one of the greatest con artists in 
recent American history. Philip Ginsburg's New York Times' 
best-selling novel tells the whole story of Audrey Marie Hilley 
in riveting detail. 

http://www.amazon.com/exec/obidos/ASIN/0446353124/qid=1018288049/sr=1-2/ref=sr_1_2/104-4074935-4203167