GADSDEN, Alabama (Reuters) - An Alabama woman accused of killing her granddaughter acted like a military drill instructor when she forced the nine-year-old to run back and forth in a yard carrying wood for almost three hours as punishment for lying about having eaten forbidden chocolates, a prosecutor said at her trial on Monday.

Joyce Garrard, 49, is accused of forcing Savannah Hardin to run non-stop at her home in Etowah County in north-east Alabama in February 2012 before she collapsed, went into seizures and died days later in hospital from dehydration and low sodium, the authorities have said.

During opening statements, Etowah County assistant district attorney Marcus Reid told the jury that Garrard acted like Sergeant Vince Carter, the drill instructor in the TV series Gomer Pyle U.S.M.C. "When paramedics arrived, little Savannah was in a T-shirt and panties, soaking wet, but cold to the touch," Mr Reid said.

He said when the police and paramedics arrived at the home, Garrard gave different accounts of what had happened: that she had fallen in the yard, she had a seizure, or she had a neurological problem.

Defence attorney Dani Bone argued that Savannah did not die as a result of dehydration, but had retained too much water in her body. "They have oversold this case to the world and they cannot prove it," Ms Bone said.

The girl suffered from unspecified medical issues that resulted in frequent doctors visits, according to court documents.

Garrard, charged with capital murder, lost a request to move the trial to a venue where the case is less well known.

The first prosecution witness was Ms Rihanna Holmes, a school bus driver who reported Savannah to her family for eating candy on the bus meant for a fundraiser.

Garrard, in a conversation with the driver captured on bus video, said "she's going to run till I tell her to stop", as punishment.

Savannah had a bladder condition and was not allowed to have anything containing caffeine, Garrard told the bus driver. "I feel partly responsible. I should have just paid for the candy bars," said Ms Holmes, who constantly wiped tears as she testified.

The child's stepmother Jessica Mae Hardin has also been charged with murder in the case, for allegedly witnessing the punishment and failing to intervene.

The girl lived with her father, who frequently travelled for work and was out of town at the time of the incident, the authorities have said.