Lawyers for Cyntoia Brown, the Nashville woman who was imprisoned at the age of 16 for killing a child predator who paid her for sex, have filed an appeal in federal court challenging her sentence.

READ: The Story Of Cyntoia Brown, A Child Sex Slave Imprisoned For Killing Her Abuser, Has Resurfaced

In a report from The Tennessean, Brown's lawyers are asking the Sixth Circuit Court of Appeals to weigh the constitutionality of her life sentence and to consider whether Brown is actually innocent because she lacked the sufficient mental capacity for a murder conviction at the time of the crime.

In the appeal, Brown's lawyers argued that she may not survive until her parole hearing at age 69 and that the Supreme Court had directed states to provide "some meaningful opportunity to obtain release."

"The half-century wait before Cyntoia Brown has a meaningful opportunity to demonstrate her 'maturity and rehabilitation' is insufficient to satisfy the minimum constitutional requirement mandated by the Supreme Court," the appeal said. "This was a seriously mentally impaired girl, subject to the immaturity and impulsiveness of all juveniles but to a much greater degree, who had been abandoned by her parents and whose only refuge was a pimp who sexually and physically abused her."

The inclusion of Brown being "mentally impaired" references an expert who testified in Brown's sentencing hearing, who noted that the now 29-year-old may have suffered from fetal alcohol syndrome disorder in utero, affecting her mental ability.

Previously, a legal expert had said that it is possible Brown could see an early release because of the newfound attention surrounding her case.

Speaking with PEOPLE magazine, University of Memphis professor Steve Mulroy said that Brown's life sentence could be commuted some time this year. Although commutations are considered a rarity in Tennessee (less than one percent of those requests are granted), Mulroy believes Brown's outcome could be different just based upon the advocacy surrounding her case.

"I think the national focus helps," Mulroy said. "There is also a compelling argument for commutation here. The governor only has a year left in office, and has tended to be more moderate than your average Tennessee Republican, who are tough on law and order issues. I suppose there's a chance it could happen."

Tennessee Governor Bill Haslam is currently looking into Brown's case. Haslam's administration has begun gathering information on Brown but said that a decision to grant her clemency is unlikely to come until this year.

Source: The Tennessean