GATESVILLE, Tex. — In January, Rosa Jimenez, an illegal Mexican immigrant, will have spent 10 years in prison in the bleak scrublands of Central Texas for a crime she says she did not commit: forcing a wad of paper towels down the throat of a toddler in her care, making him choke and ultimately die.

She sits here in the Mountain View Prison Unit, a maximum-security facility for women, folding prison laundry, reading Bible stories and praying for exoneration while her two children are brought up by foster parents. To some, Ms. Jimenez has become a symbol of the inequality of the American criminal justice system — a process that began with a 2007 Mexican documentary that showed the prosecutor saying of Ms. Jimenez, “Despite being from Mexico, she’s very intelligent,” and that enraged the mayor of her hometown.

At her trial, the defense’s medical witness — a forensic pathologist who was not an expert in pediatrics or choking, who cost far less than the experts her lawyers originally sought and who swore at prosecutors in the courthouse hall (and later acknowledged doing so on the witness stand) — came off as an amateur.

Thousands of poor Mexicans are in American prisons and, like Ms. Jimenez, were heavily outlawyered and outspent at trial. Her story is that of many like her, yet she has been cast as a kind of hero by some.