PHOENIX (AP) — An Arizona woman who put her 17-month-old daughter in a stroller, pushed her into the desert and left her to die on the nation’s largest American Indian reservation has been sentenced to 20 years in prison.

U.S. District Judge David Campbell said Ashley Denise Attson, 23, committed an “intentional, cold-hearted, horrendous killing of an innocent child,” imposing Monday the high end of a sentencing range detailed in a plea agreement with prosecutors.

Attson had pleaded guilty to second-degree murder in the September 2016 killing on the Navajo Nation. Her defense attorney, Ashley Adams, did not immediately return a call for comment.

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Attson left her daughter in the desert for four days and nights before retrieving the body and burying it in an animal hole, the U.S. Attorney’s Office for Arizona said Tuesday in a statement.

“Over the next few days, she met friends for ice cream and posted pictures of herself on Facebook,” the statement said.

The child was born with methamphetamine in her system and was in the custody of tribal social services most of her life before Attson regained custody about two months before her daughter was killed, prosecutors said.

U.S. attorney’s spokesman Cosme Lopez declined to comment on the motive for the killing and said he could not provide additional information on circumstances of the child’s death.

Lopez also said policy prohibited release of the child’s name because she was a juvenile. Court documents refer to her as “Jane Doe.”

The plea agreement said the maximum punishment that Attson could have received under her guilty plea to the murder charge was life in prison, and a former tribal prosecutor said she was troubled that Attson received a 20-year sentence.

The child no doubt was afraid, in physical distress and “needing the one person who is supposed to care for her the most, that being the mother,” said Bernadine Martin, a former chief prosecutor for the Navajo Nation. “And 20 years is simply not enough.”