Lawyers for jailed child sex trafficking victim Cyntoia Brown filed an appeal Monday challenging the now 29-year-old’s sentence. Brown remains behind bars in Tennessee, serving a life sentence for murder, committed when she was 16-years-old.

An appeal filed by Brown’s lawyers this week challenged the constitutionality of the sentence and asked the court to consider whether Brown could be innocent because she “lacked the sufficient mental capacity for a murder conviction at the time of the crime,” The Tennessean reported.

Brown was convicted of shooting and killing 43-year-old Johnny Allen, a real estate agent who reportedly solicited her for sex. During her 2004 trial, Brown testified that she was repeatedly raped, choked and beaten and forced into prostitution by her pimp. Her lawyers argued that her experiences led her to shoot Allen. Brown was found guilty of prostitution and murder.

Celebrities, including Rihanna and Kim Kardashian, rallied around Brown and drew attention to her situation in recent months. The hashtag #FreeCyntoiaBrown went viral at one point with those on social media calling for her to be released from prison.

“The system has failed,” Kardashian wrote on Twitter in November. “It’s heartbreaking to see a young girl sex trafficked then when she has the courage to fight back is jailed for life! We have to do better & do what’s right.”

Under her current sentence, Brown would only be eligible for parole after serving 51 years in prison, when she would be 69-years-old. In the appeal, her lawyers argued that a life sentence for juveniles is unconstitutional and that she may not survive until that age.

“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, according to The Tennessean. “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 state was expected to respond to the appeal in February.