PHOENIX -- A woman convicted of bludgeoning her husband to death with a hammer made a tearful plea for mercy Thursday, telling the jury deciding her fate that she is sorry for her actions and wishes she could go back and undo the pain she caused.

Marissa Devault, 36, broke down in tears and repeatedly lost her composure as she spoke to the jury in the penalty phase of her trial. The same jury that convicted her of first-degree murder is deciding whether she should get the death penalty or a life sentence.

"I don't know if I can be useful to anybody in this world or in any way ... but I would like the opportunity to try," she said.

Devault was found guilty last week in the killing of Dale Harrell, who suffered multiple skull fractures in the January 2009 attack in the couple's home in the Phoenix suburb of Gilbert. The penalty phase began this week and featured emotional testimony from Devault's daughters a day earlier.

Devault clasped a tissue, removed her glasses, took deep breaths and fought back tears for more than 10 minutes. She expressed regret for inflicting pain on her daughters, saying "this goes into generations that don't even exist yet."

"I can't do anything more than say I'm sorry. I can't push the back button. I can't bring him back. I can't fix everything that was wrong," she said.

She also looked ahead to prison and hoped that she could "talk to someone" and help them make a better choice.

Prosecutors say she killed her husband in a failed bid to collect on a life insurance policy to repay more than $300,000 in loans from her boyfriend, a man 20 years her senior she met on a sugar-daddy website.

Devault said she killed Harrell in self-defence and told investigators he had physically and sexually abused her in the past. She would become the third woman on Arizona's death row if the jury opts for the death penalty.

The case had similar circumstances as the Jodi Arias trial that played out in Phoenix one year ago, including a brutal killing of a lover, claims of self-defence and salacious elements such as Devault's one-time job as a stripper.

But the judge in this case made extensive efforts to keep the trial from becoming the spectacle that enveloped the Arias case.