A North Carolina court sentenced on Thursday to 18 years prison term an American woman who killed her 10-year-old disabled Australian stepdaughter.

Elise Baker, 43, pleaded guilty to the second-degree murder, obstruction of justice and other charges unrelated to the death of Zahra Baker, who had her leg amputated after a bone cancer battle when she was 5 and had to use a prosthetic leg and hearing aids.

About a year ago, Zahra was reported missing from the Baker home in Hickory, North Carolina. Ms Baker made it appear that Zahra was kidnapped and even came up with a forged ransom letter as proof.

Ms Baker later changed her story and told police that Zahra died on Sept. 24. She claimed Zahra was sick and went to bed after an afternoon meal, but after one hour when Ms Baker checked on the girl, she was allegedly unresponsive. Later, Ms Baker pointed to her husband as the one who dismembered Zahra, but investigators found proof that Mr Baker was working on a landscaping project on the morning he allegedly killed his daughter.

However, police eventually discovered Zahra's dismembered body which had parts scattered on bushland outside Hickory. Even if some of the girl's body parts were not found, autopsy done on her bones showed cutting tool marks which are marks of dismemberment.

Zahra and her father, Adam Baker, migrated from Queensland to North Carolina in 2008 after Mr Baker met Elise online. He was separated from Zahra's biological mother, Emily Dietrich, who is a resident of Wagga Wagga, New South Wales.

Ms Dietrich flow to North Carolina for the hearing held in the Catawba County Courthouse. The court pushed back by one day the original Wednesday hearing to accommodate Ms Dietrich.

When Ms Dietrich heard details of Zahra's death, she called Ms Baker "pure evil" and the crime a "heinous act."

"My only hope now is she (Zahra) is in a place where she never feels pain.... In a place where she can feel my love," Ms Dietrich was quoted by AP.

"There are no words to explain the hate I have for you," Mr Baker told his second wife.

"I trusted you with the most precious person in my life.... Zahra will never get to go to high school, never have a real boyfriend, never get married and never have children," Mr Baker said.

Mr Baker is also facing several criminal charges, but it is not related to Zahra's death. He found the 18-year sentence quite a light penalty for second-degree murder.

Ms Baker apologized for the pain she caused and agreed to plea guilty to bring closure to her stepdaughter's death. Although medical examiners said that Zahra's death was caused by "undetermined homicidal violence" the reason why Ms Baker killed her remains unanswered.

There were witness accounts that Ms Baker beat Zahra, who once attended school with two black eyes. Investigation showed that Ms Baker herself led a troubled life, constantly moved homes and had seven marriages, some of which overlapped. Her former husbands told AP that Ms Baker had a history of beating her three children and social service agencies in different counties have probed the incidents.