A woman who pleaded guilty to killing her stepdaughter 25 years ago was formally acquitted by an Ontario appeal court on Monday.

Maria Shepherd pleaded guilty in 1991 to manslaughter after the death of her three-year-old stepdaughter Kasandra Shepherd. She took the plea based on evidence from Dr. Charles Smith – a now-disgraced pathologist.

At the time, Smith was considered to be an unassailable expert. However, a later review and public inquiry of his work found that he had made numerous errors in several cases, with some leading to wrongful convictions. He was stripped of his medical licence in 2011.

“I have raised my children being known as a baby killer, killing their sister,” Shepherd told CTV Toronto on Monday.

After she was accused in her stepdaughter’s death, the authorities “made it very clear that there was nobody else out there that was willing to challenge Smith because he was right,” she said.

“He wasn’t wrong. He was infallible.”

After she was formally acquitted on Monday, Shepherd told reporters she was relieved to finally have a chance to live with some degree of normalcy.

"As a family we are elated, but this didn't come without 25 years of a lot of quiet tears and anguish at home," she said from the steps of the courthouse.

"We get an opportunity now to have a life together," she added, noting she will now be able to spend time with her children and forthcoming grandchildren without restrictions or supervision.

At the time of her guilty plea, Shepherd was sentenced to two years less a day in prison. She gave birth to her fourth child in prison.

Court documents show that Kasandra had been vomiting and became unresponsive in April 1991 after a period of ill health. She died two days after being admitted to hospital. Smith concluded that Kasandra had died from trauma due to at least one blow of "significant force" to her head.

Shepherd, who was 21 at the time, told police she had pushed the girl once, with her wrist and watch hitting the girl on the head. However, she didn't believe the blow could have killed her.

Shepherd told reporters on Monday that she pleaded guilty because everyone involved in the trial viewed Smith as a type of "god," whose opinion was unquestionable.

She said even her own defence lawyer at the time consulted an outside expert, who agreed with Smith's opinion. As a result, she agreed to plead guilty to manslaughter rather than risk conviction at a later trial.

However, Shepherd said she always knew she was innocent.

"I never did anything but care for Kasandra," she said, with her husband and children standing in support behind her.

Forensic experts now believe that Kasandra may have had a previous brain injury, which may have caused seizures. They also believe that she may have suddenly developed a seizure disorder that could have killed her.

Shepherd described how the guilty plea had devastating consequences for her and her family. She said she was labelled as a "baby-killer" and couldn't look for employment due to her criminal record.

"You hide yourself, you try and operate and hope that people don't recognize you," she said, describing how she coped with the ordeal.

Shepherd said despite everything she and her family have been through over the past 25 years, she has come to forgive Smith.

"I'm not sure what was going on in Mr. Smith's head. There must be something extremely troubling for somebody not to do it once or twice – we're talking a least a dozen people that he has done this to," she said.

"I forgive Charles Smith, because it's going to be less of a weight, and my family and I can carry on."

'The system tends to fight you all the way'

Shepherd's defence lawyer James Lockyer, with the Association in Defence of the Wrongly Convicted, said he was pleased that justice was finally served. However, he warned that these types of errors can still happen because the justice system often relies on expert opinions.

"Absolutely, no question," Lockyer said on Monday after the acquittal. "There are plenty of forensic scientists out there, including pathologists, who can and will make errors.

"They can all get it wrong. Even the best can get it wrong."

He also noted that the process of overturning a wrongful conviction is often long and expensive, meaning many people do not end up seeking them.

"If there's anything to learn from this, it's that it's very difficult to establish that someone has been wrongly convicted," he said. "The system tends to fight you all the way."

With files from The Canadian Press and a report from CTV Toronto’s Austin Delaney