A southern Alberta mother who killed her daughter by drugging her and burning her alive inside a car has pleaded guilty to second-degree murder.

Amber Lucius, who was nine, was found dead in a car on a rural road near Sundre, about 100 kilometres northwest of Calgary, in September 2014.

Amber lived in a rural area near Wetaskiwin and had been visiting her mother, Laura Coward, on the Labour Day long weekend.

She was supposed to have been returned to her father, Duane Lucius, two days before her body was found.

Laura Coward

Laura Coward, 48, was charged with first-degree murder in the death of her nine-year-old daughter Amber Lucius. She pleaded guilty to second-degree murder on Thursday. (Jane Fletcher)

"I've lost my daughter and I'll miss her," said a distraught Lucius outside the courthouse Thursday.

"She was a fun-loving little girl. She had a lot of life ahead of her and I wish she'd still be here."

Coward was originally charged with first-degree murder.

But defence lawyer Jim Lutz and Crown prosecutor Mac Vomberg negotiated a plea, which was entered in a Calgary court Thursday.

In the court documents released Thursday, it was revealed for the first time publicly that Coward admitted to drugging her daughter and setting the car on fire while she was alive.

It happened on Aug. 30. Coward separated Amber from her elder half-sister and a group of friends at about 10:30 p.m.

She told them she was going to take Amber star gazing, but drove her daughter to pick up some Timbits and then to a rural road.

Coward gave her daughter sleeping pills that she'd stolen from a friend.  While her daughter was unconscious inside the SUV, Coward stole a propane torch from a nearby trailer and set it on fire. The child, burned alive, died of smoke inhalation.

Amber had been at the centre of a lengthy custody battle between her parents, according to court documents.

Coward and Lucius separated in October 2007.

Despite 10 court orders directing Coward to allow Lucius access to his daughter, Coward did not comply and Lucius was granted full custody of Amber in June 2013.

A hang-up 911 call on Sept. 2, 2014, led RCMP to the car, which was parked on a friend's property. Officers arrested Coward as she emerged from the friend's home wrapped in a blanket.

A sentencing hearing will take place in March.

With files from Kate Adach