PEABODY — Jennifer Ward was found guilty of involuntary manslaughter yesterday for brutally shaking and slamming her 9-month-old daughter to death nearly two years ago.

The verdict means Ward, 39, could face up to 20 years in prison when she is sentenced on Monday in Salem Superior Court for the November 2007 death of her baby, Jocelyn Mae Ward-Anderson. She had been charged with first-degree murder, which would have meant a life sentence.

Ward whispered "thank you," grabbed her lawyer's hand and then looked back at her parents but showed no emotion when the jury foreman read the verdict just after 3 p.m.

The baby's paternal grandmother, Mary Johnson of Lynn, who cared for the child for several months while Ward was taking part in drug treatment and parenting classes, expressed relief that Ward was found responsible for the child's death.

"It's something," she said, adding that she'll have more to say in a victim-impact statement Monday.

Ward's mother, Cheryl, who cared for Jocelyn most weekends after she was returned to Ward's custody, burst into tears in the courtroom upon hearing the verdict.

Prosecutor Kate MacDougall had hoped to convince jurors that Ward was guilty of first-degree murder either by premeditation or extreme atrocity or cruelty. She described a prolonged series of assaults on the baby, including grabbing and twisting her arm hard enough to snap it, then shaking the baby violently, causing two more fractures near her shoulders and extensive brain damage, and then finally slamming the child against something hard enough to crack her skull.

MacDougall argued that the attack, on Nov. 18, 2007, was motivated by Ward's anger at the teething baby after she had been fussing for 21âÑ2 hours.

Ward's defense lawyer, Thomas Barrett, insisted that Ward hadn't harmed the child at all, suggesting instead that it was a longtime family friend who planned to stay with Ward that night, or that perhaps medical personnel or a rare bone disease caused her injuries.

Jurors interviewed outside the courthouse after the verdict said they quickly rejected Ward's defense.

But getting to a final verdict from among the options they were given — first-degree murder, second-degree murder and manslaughter — proved a bit harder.

The jury, which was initially split on the question of murder versus manslaughter, deliberated for about eight hours over two days.

Yesterday morning, the jury asked for a written copy of the instructions for each of those options.

In the end, it came down to "two words, malice and intent," juror Roberta Rimari of Beverly said.

"None of us believe she intended to kill her baby," said Rimari, who described the case as "very difficult."

"I think we came to a fair conclusion," she said.

Ryan Suzar of Salisbury said he initially believed Ward was guilty of first-degree murder. "There were several of us" who felt that way, he said.

But as he listened to fellow jurors, he came to share the view that the prosecutor hadn't proven Ward intended to kill the baby.

"Nobody was there with her. Nobody knows how she was feeling," Suzar said. "Toward the end (of deliberations), I think I kind of wasn't as sure as I was in the beginning."

What about the phone call hours before the assault, in which Ward berated the child loudly?

Suzar said he and other jurors felt it was too remote in time to connect to the assault on the baby later that night.

Jamie Foote of Ipswich, another juror, said he also eventually came to the conclusion that there just was not enough proof that she intended to kill her baby.

Rimari called yesterday "one of the hardest days I've ever spent with a group of people."

Juror Bob Hughes of Andover called the trial "the most difficult two weeks I've ever been through. The whole thing was very difficult."