EDINBURG, Texas—A nearly half-ton Texas woman charged with killing her 2-year-old nephew couldn’t have beaten the boy to death because of her weight, her attorney said Tuesday.

The mother of the dead boy is also sticking up for Mayra Rosales, her nearly 1,000-pound sister who is charged with capital murder and is under house arrest because Hidalgo County Jail cells are too small and lack the medical resources she requires.

An attorney for Jamie Rosales, who is charged with injury to a child for leaving her son in the care of his bedridden aunt, said his client believes the death was possibly caused by the morbidly obese woman rolling onto the toddler. “It was an accident,” Oscar Vega told The Associated Press.

Mayra Rosales was indicted last week in the March 18 death of Eliseo Gonzalez Jr., who prosecutors say was hit twice in the head while being watched by his aunt.

A state district judge on Monday agreed not to send Rosales to jail provided she wear a global positioning system tracker until her trial.

Sergio Valdez, Mayra Rosales’ attorney, said the 27-year-old lacks the movement in her arms to have killed the child, calling it an “impossibility.” “She is not physically capable of having committed those acts,” Valdez said.

Valdez said Mayra Rosales suffers from a thyroid problem that has caused her to put on hundreds of pounds over the past three to four years. He said she finished high school, took some vocational classes and weighed about 250 pounds before her condition began to worsen.

Valdez said Mayra Rosales has been bedridden for more than a year, gets visits from a doctor and has a significant other who helps take care of her.

“It’s been a gradual,” Valdez said. “Her movements have become less and less.”

Hidalgo County Sheriff Lupe Trevino has argued that incarcerating Mayra Rosales would be impossible because the county jail does not have a cell large enough to hold her or medical staff equipped to handle her medical needs.

Vega said Jamie Rosales has a learning disability and will plead not guilty. He declined to say where his client was the day of her son’s death, but said he knew of no order forbidding the boy to be watched by his aunt.

Vega said any documentation that may exist was a state recommendation and not the law. He called the allegations “totally bogus” and said the sisters remain close.

“She doesn’t believe her sister intentionally did anything to her child,” Vega said.