An American man whose infant daughter was kidnapped in the United States 20 years ago says he is pleased his ex-wife has received the maximum penalty for her crime.

In 1994 Dorothy Lee Barnett, 54, fled to Australia with her daughter but was arrested on Queensland's Sunshine Coast in 2013 for parental kidnapping and falsifying passport documents.

She was deported to the US last year and yesterday pleaded guilty to the charges in Charleston, South Carolina and sentenced to 21 months' jail.

The girl's father Harris Todd said he was pleased the judge condemned the actions of his former wife.

His lawyer, Graham Sturgis, said his client was very pleased with the outcome and was glad it was over.

He said Mr Todd was looking forward to growing his relationship with his daughter, who was now studying in Australia.

"There's no amount of time that would make up for having lost his daughter for 20 years," Mr Sturgis said when asked if the sentence was appropriate.

"It's not an eye for an eye, a tooth for a tooth to make this right."

Prosecutors said Barnett vanished with her baby girl during a court-approved visit in South Carolina after her ex-husband was granted legal custody of their child in a contentious divorce.

Barnett moved overseas, remarried and changed her name to Maria Geldenhuys, according to court records.

She also renamed her daughter from Savanna to Samantha and told her child that Barnett's new husband was the girl's father, prosecutors said.

In tearful testimony on Monday, the daughter, now 21, said she was shocked to learn just a few years ago that she had another identity.

"I've had the opportunity to meet with my biological father for a few hours," she said.

"It was an experience that I cannot describe in one word."

'Calculated, methodical crime'

District court judge Richard Gergel described the kidnapping as a "calculated, methodical crime" and that a full sentence was appropriate.

"There were no winners in this, it was a horrible tragedy," he said.

Mr Sturgis said the matter had been resolved legally but he hoped Mr Todd would have the opportunity to spend time with his daughter.

The court heard some poetry written by Mr Todd both before and after his daughter was kidnapped.

He wrote this poem, just two months before his daughter was taken away by her mother: