Melissa Weeks of New Glasgow, Nova Scotia, was arrested Monday, the day after her husband, a recent widower, became violently ill. She and Fred Weeks, 75, had gotten married just weeks ago, the Canadian Broadcasting Corp. reported.
The CBC said Weeks was convicted of killing a previous husband and spent time in jail for stealing from a man she was living with in Florida.
Weeks, who is jailed in Sydney pending a Friday hearing, is accused of "administering a noxious thing." Prosecutor Dan MacRury said authorities will oppose bail for Weeks.
"We are of the view that one, there is the likelihood that she may commit other offenses, and also that we believe she may be a flight risk," he said.
Fred Weeks is now out of the hospital, the CBC said.
Melissa Weeks served two years of a six-year prison sentence for killing a previous husband, Gordon Stewart of Prince Edward Island, in 1991.
She later moved to Florida where she met Robert Friedrich. They married in Nova Scotia in 2000. The next year, his family noticed his health started failing and he died of cardiac arrest in 2002. No charges were filed in his death.
She then met Alex Strategos through the Internet and he wound up in a hospital with a head injury the day they moved in together. She ultimately served five more years in prison for stealing from him.
Strategos, now 81 and living in Pinellas Park, Fla., told the BBC he wasn't surprised to hear she's in trouble with the law again.
"I just think she's a little bit old to be playing games, that's all," he said Tuesday.
"She's a nice woman, she treated me all right until she started giving me drugs."
Weeks was released from prison in 2009 and deported to Canada.
Members of Congress to keep receiving porn magazine
Putin thinks Obama would save him if he were drowning