Penny Boudreau sobbed as she apologized in court Friday. She was sentenced to life in prison with no parole for 20 years after pleading guilty to second-degree murder. (CBC)

A woman from Bridgewater, N.S., has been handed a life sentence with no parole eligibility for 20 years for strangling her only child after her boyfriend gave her an ultimatum.

Penny Boudreau, 34, pleaded guilty Friday to second-degree murder in the death of 12-year-old Karissa Boudreau.

The girl's frozen body was found on the outskirts of Bridgewater on Feb. 9, 2008, about two weeks after her mother reported her missing.

Boudreau, wearing a black T-shirt and jeans, told the court, "I'm sorry."

When asked about the apology, Paul Boudreau, Karissa's father, said bluntly: "Crocodile tears."

"Justice has been served," he added.

Justice Margaret Stewart, who handed down the sentence at the Nova Scotia Supreme Court in Bridgewater, said the horrible crime merited a harsh sentence.

"You can never call yourself mother in conjunction with Karissa's name again," Stewart said.

Karissa's relatives sobbed loudly as Crown attorney Paul Scovil read out the grim details of the girl's final moments in an agreed statement of facts.

The court heard that Boudreau's boyfriend, Vernon Macumber, told her she had to choose between him and her daughter if she wanted to save their relationship.

Carried body to river

It was dark and snowy on Jan. 27, 2008, when Boudreau drove the girl to a remote spot on William Hebb Road in Hebbville, near Bridgewater.

They got out of the car and argued. Boudreau tackled her daughter, knelt on her chest and strangled her with a length of twine.

Boudreau could feel the girl's hands digging into the ground as she struggled.

Karissa's last words were, "Mommy, don't."

Boudreau then put the body in the car and threw away the twine in a coffee cup.

She drove to a spot along the LaHave River, and as she dragged the body, pulled down Karissa's pants to give the impression the girl had been sexually assaulted. She then rolled the body down an embankment.

Karissa Boudreau, 12, was a Grade 6 student at Bridgewater Elementary School. (Bridgewater police)

Boudreau later tossed several pieces of Karissa's clothing in the garbage can at the local swimming pool.

When she got home, she told police her daughter had run away. She also called friends and teachers to spread the story.

Stewart had harsh words for Boudreau.

"The words, 'Mommy, don't' from a trusting and loving Karissa are there to haunt you for the rest of your life," she said.

Paul Boudreau is still trying to comprehend what happened. Karissa was living with him at one point but moved to Bridgewater to be with her mother.

"I can't call it anything other than a senseless act," said Boudreau, adding his ex-girlfriend had options.

"Had I known this was going to happen, I would have never let her go back. But what parent is going to say, 'No, you can't go back and see your mother,'" he said.

Penny Boudreau was charged with first-degree murder in June 2008. At the time, police said they believed Karissa knew her killer.

Scovil said Boudreau had two motives: to save her faltering relationship with Macumber and keep Karissa from publicly calling her a bad mother.

He said he agreed to the lesser charge of second-degree murder to give the family some closure and avoid the uncertainty of a trial.

Murder carries an automatic life sentence. Both the Crown and defence recommended parole eligibility after 20 years.

"All in all, it was the right thing to do," Scovil said.

As for Macumber, Scovil said there was no evidence he wanted his girlfriend to kill her daughter. He said Boudreau made it clear that she was solely responsible.

"We suspected very strongly that he must have had an idea. But there was no evidence to suggest that he either had concrete evidence or assisted in any way," Scovil said.

Undercover police investigation

The grim truth of what happened to the girl came out as a result of an undercover police investigation.

Boudreau gave the details to officers posing as organized crime bosses, who said they could help her destroy evidence held by police.

Karissa's story has gripped the small Nova Scotia community ever since her mother made a tearful plea at a news conference for her daughter's safe return.

Boudreau said they had had a fight in the parking lot of a grocery store, and when she came back to the car, Karissa was gone.

Several searches of the area turned up no sign of the young girl.

Two weeks later, a passerby discovered Karissa's frozen body on the bank of the LaHave River.

Paul Boudreau said he had suspicions about his ex-girlfriend from the moment Karissa was reported missing.

"Any parent knows their child, and when a child does something way out of character, you know from Day 1 it's not true," he said.

Rumours had been circulating around Bridgewater, too.

Wendy Rhodenizer, a resident who helped organized this week's candlelight vigil, said the town is going to have an even tougher time healing now that the details of Karissa's death are out.

"We'd heard some really vicious rumours at the beginning, and we didn't know what to believe," she said. "I will say one thing, I'm extremely impressed with the investigators in this."

Senior officers with the RCMP and local police say hardened investigators were reduced to tears during their long undercover inquiry.

Though Penny Boudreau was sentenced to life with no eligibility for parole for 20 years, she can apply for early parole after 15 years under what is known as the faint-hope clause of the Criminal Code.