An East Feliciana Parish woman avoided a possible death sentence by pleading guilty Monday in the killing of a woman and her 3-year-old son and the attempted murder of two of that woman’s other children at a BREC park near Zachary in 2008.

Trendall Lashel Matthews, 25, of Jackson, pleaded guilty to two counts of first-degree murder in the slaying of her cousin Jessica Johnson Palmer and Juan Palmer Jr. in exchange for a sentence of life in prison at the Louisiana Correctional Institute for Women in St. Gabriel.

Matthews, who was scheduled to stand trial July 25, agreed Monday to testify against her co-defendant and boyfriend, Dominique Dantoni Smith.

Smith, 30, of Wilson, and Palmer, 23, of Baker, were once romantically involved and had a child together.

Smith was the target of a paternity and child-support petition involving Palmer’s daughter, Lindsay Paige Johnson, according to West Feliciana Parish court records. Palmer filed the petition against Smith in November 2006.

Matthews also pleaded guilty Monday to the attempted first-degree murder of Lindsay Johnson and her younger sister, Robbyn Palmer, who were left for dead May 4, 2008, in Doyle’s Bayou Park on Pride-Port Hudson Road.

Lindsay was 4 years old at the time and had her throat slit. Robbyn Palmer was 6 months old at the time but was not injured in the attack.

State District Judge Tony Marabella sentenced Matthews to life in prison on each first-degree murder charge and 50 years in prison on each attempted first-degree murder charge. He ordered the sentences to run concurrently.

“I’ve seen a lot of things,’’ noted Marabella, who practiced law for 30-plus years before becoming a judge more than eight years ago. “I can’t imagine the horror that those children and that woman went through. …’’

Prosecutor Darwin Miller told the judge that Smith and Matthews met Palmer and her children at the park, and that Smith and Palmer were talking about paternity in a remote and isolated area of the park when Matthews heard screams.

Miller said an altercation and argument then erupted involving the three adults, and Smith knocked Palmer to the ground and eventually cut her throat.

While Palmer was on the ground, the prosecutor said, Matthews “placed her feet on Jessica Johnson Palmer to hold her down’’ while Smith continued to cut her.

Matthews also confessed that she was holding Juan Palmer Jr. and Lindsay Johnson when Smith cut them, Miller said, adding that Juan Palmer Jr.’s body was burned.

The prosecutor said a baseball bat also was used in the attacks, although Matthews denied that claim.

Matthews, flanked by defense attorneys Fred Kroenke and Scott Collier, acknowledged that the rest of what Miller said was true but declined the judge’s invitation to address the court.

“She finally accepted responsibility for what she had done,’’ Kroenke said after court. “It was very difficult. We’ve been at it for three years.’’

Relatives of the victims were in the courtroom but declined comment afterward.

Matthews signed a “contract for life’’ in which she waived all appellate, post-conviction and habeas corpus rights to seek review of her guilty pleas and life sentence.

“This ends the matter. You can’t appeal,’’ Marabella told her.

Miller said it was the will of the victims’ family that Smith and Matthews be offered a chance to plead guilty and admit their guilt in exchange for life sentences.

Miller said such an offer was previously made to Smith, but the offer expired Monday.

Prosecutors intend to seek the death penalty against Smith, who does not have a trial date. He also is charged with two counts each of first-degree murder and attempted first-degree murder.

Marabella ruled Monday that jurors in the case will be allowed to hear from an East Baton Rouge Parish sheriff’s deputy, a paramedic, a registered nurse and a doctor what Lindsay Johnson told them shortly after she was found in the park on May 5, 2008.

Defense attorneys had argued that efforts to gain information from Lindsay Johnson cannot trump the right to confront and cross-examine accusers.

Miller has not ruled out putting Lindsay Johnson on the witness stand.