A Calgary woman who admitted to killing her 26-day-old son has been sentenced to five-and-a-half years.

Shelby Herchak, 22, received credit for time she's already spent in custody, meaning she now has two-and-a-half years of her sentence left to serve. She will be eligible for release after serving two-thirds of her sentence, meaning she may be released before she turns 25.

Herchak was originally charged with second-degree murder, but pleaded guilty to a lesser charge of manslaughter.

She was just 18 when her son Daniel died in 2010. An autopsy determined that Daniel died from blunt force trauma to the head, but it is not known how he was injured.

Her lawyer sought a four- to five-year sentence for Herchak, but the Crown argued for a sentence of seven to eight years.

In her judgment, Justice Kristine Eidsvik said the severity of the case didn't warrant a sentence as long as prosecutors wanted.

Crown attorney Daniel Brunnen told reporters outside the courthouse that it would take some time to process the ruling.

"It was quite a thorough judgment, so still need some time to process it and just digest what she's placing her judgement (in)," Brunnen said.

Defence lawyer Kim Ross said he believed it was appropriate.

"Overall I think it's a good sentence, it was decided with what a lot of what we had submitted in terms of case law and range of sentence," he said.

Eidsvik said that while Herchak did kill her son, there's no evidence she abused him prior to his death. She also acknowledged that Herchak was remorseful.

During her sentencing hearing last month, Herchak tearfully apologized to her parents and the community.

Herchak's aunt, Susan Lloyd, said she would have preferred to have seen her niece receive a longer sentence.

"She gets extra credit, she gets time served. I would have liked to have seen eight years," Lloyd said. "She would have been more mature, maybe she would have seen the severity of her actions… and she would actually get the help because it would be given to her."

Herchak's relatives said she was too young and unprepared to be a mother, and went out partying shortly after her son was born.

Ross said that his client is relieved that the case is over.

"She's glad that this is all over now. It's been a long road for her, and an emotional one," he said. "I think she's happy to see it come to an end, and she'll put this behind her and move on with her life.

He said he believes Herchak will take the judge's advice and go back to school and get help for her anger problems.

With a report from CTV Calgary's Ina Sindhu