Kate Knight, 28, from Wirral, was convicted of attempting to murder Lee Knight by lacing his food with ethylene glycol, had her appeal rejected by the Court of Appeal.
The jury heard Knight used internet search engine Google to find a method of killing, settling on anti-freeze.
Knight served the anti-freeze in red wine and Indian takeout on their wedding anniversary.
In a separate murder trial:
A detective testified in a US court that a laptop computer taken from the home of a British man accused of killing his wife and nine-month-old daughter was used to search online on "how to kill with a knife", four days before the slayings.
Medford police Detective Lawrence James, a computer expert, said the Google search was done on January 16, 2006.
Neil Entwistle has pleaded not guilty to murder charges stemming from the killing of his 27-year-old wife, Rachel, and their daughter, Lillian Rose, in their rented home in Hopkinton, Massachusetts on January 20, 2006.