Joan Faye Hartman, who was convicted of manslaughter in 22nd Judicial District Court last month for fatally stabbing her son’s girlfriend at their Slidell home, was sentenced to 35 years in prison Friday by Judge Scott Gardner.

Gardner handed down the sentence after Hartman’s lawyers spent several hours making a case for a more lenient punishment.

The maximum penalty for manslaughter is 40 years.

Hartman, who killed Tanya Knower in 2012, will get 2 ½ years of credit for time served, but she will have to serve 85 percent of her sentence, which means she cannot be released until she is 84. Hartman is 56 and suffers from chronic obstructive pulmonary disease, and her attorney, Martin Regan, said she has only 30 percent of her heart function.

“She received a life sentence today,” Regan said.

Knower’s mother and stepfather made victim-impact statements in court Friday about the 27-year-old victim, whom they described as a good daughter and mother who had worked in day care and was pursuing a college education. She had two young daughters with Hartman’s son, Richard.

Hartman’s attorneys called a number of witnesses for the sentencing phase, including a psychiatrist who testified about the potential negative effects of the drug Xanax. Hartman had testified that Knower was addicted to the drug and became violent when using it.

They also presented testimony about Hartman’s conduct in jail. They said she earned more than 100 certificates for completing programs and that she counseled other inmates.

Regan said there was evidence that Hartman was acting in self-defense and pointed out that Knower had stabbed the older woman eight years before.

Hartman had no previous arrests or convictions, Regan said, and he presented testimony from a psychiatrist who said she was extremely unlikely to ever again behave violently.

Hartman’s attorneys are pursuing an appeal, and Regan said he is optimistic a new trial will be granted because the prosecution brought in a toxicologist as a witness at the trial whom the defense did not know about.

Follow Sara Pagones on Twitter at @spagonesadvocat.