CALGARY -- An Alberta woman who drugged and killed her nine-year-old daughter begged the girl's father and her own family and friends for forgiveness at a sentencing hearing Friday.

Laura Coward, 50, pleaded guilty last month to the second-degree murder of Amber Lucius and is facing an automatic life sentence with no chance of parole for at least 10 years.

"I just want to say that every day, at every moment I miss my children ... loved them more than everybody will ever understand," Coward said through tears.

"I want to say to the father, my family, friends that I'm responsible for my choices and I beg for their forgiveness and I plead for your mercy," she told Justice Scott Brooker.

Coward's former husband, Duane Lucius, said earlier in a victim impact statement that he would never forgive Coward for the pain she has caused.

"I try to be strong for my family and friends," Lucius told Calgary Court of Queen's Bench. "I feel upset (about) how someone could do something like this to a little, innocent girl with a whole life ahead of her."

Holding a picture of Amber, Lucius told court he misses his daughter's warm hugs and thinks about her every day.

"I gave her mom time to spend with her, but Laura never thought it was enough. I will never forgive her and I will never forget my daughter Amber."

The girl was reported missing Aug. 31, 2014, and her mother was arrested two days later near Sundre in west-central Alberta. She was standing outside a burned truck in which her daughter's body was discovered.

Coward had Amber for the weekend and, on a trip to a remote area, gave her a toxic but non-lethal dose of a prescription sleeping medication. She mistakenly thought Amber was dead and filled the truck -- with Amber unconscious inside -- with paper and plastic totes before setting it on fire with a propane torch and closing the door.

An autopsy suggested the girl died of a combination of hypothermia, smoke inhalation and carbon monoxide toxicity.

A police officer who came upon the burned vehicle saw a handwritten note on the outside of the driver's door that read: "Help me. It was an accident. Locked keys in."

Crown prosecutor Jillian Pawlow urged the judge to require Coward spend 20 years in custody before she can seek parole.

"The Crown submits that the accused's primary motivation was revenge-motivated, meant to inflict the most serious and permanent pain and anguish on Duane Lucius by depriving him of his only daughter," said Pawlow.

Coward's lawyer, Jim Lutz, argued his client should be allowed to apply for parole in 10 to 12 years. He suggested her guilty plea was an indication of remorse.

Coward is to be sentenced March 10.

A letter from Dale Coward on behalf of his sister was read into the court record.

"I have to believe that she has a mental-health illness in order for me to wrap my head around what has happened," Dale Coward wrote.

"I'm hoping during the time Laura is in jail she will get the help needed to recover from her illness ... God willing I may be around when the time comes for Laura to reintregrate into the community and make a life.

"No matter what happens she's still my sister."

Court documents described a bitter divorce between Coward and Lucius. A custody tug-of-war over their daughter had continued up until the girl was found dead.

In June 2013, a judge had named Lucius as Amber's primary caregiver and the girl moved back to his parents' farm with him. Coward and another daughter from a previous marriage moved to a nearby rural property to be closer to Amber.

"This is a senseless and unimaginable nightmare. A stern message is required to deter both her and others that might find themselves in acrimonious proceedings," said Pawlow.

"This murder was not an accidental killing. She knew her actions were guaranteed to cause death."