It's been 13 years since Cyntoia Brown was sentenced — at the age of 16 — to life in prison for the killing of a man who had picked her up for sex. But this week, thanks the power of celebrities on social media, the case rose to national attention again, and Brown's lawyer said she was "shocked" at the renewed interest.

Brown, now 29, was imprisoned in Tennessee following her trial and life sentence for the death of 43-year-old Johnny Mitchell Allen, who had paid her for sex. Advocates for Brown and her lawyer say she is the victim of sex trafficking and her sentence was too extreme, given her age and circumstances.

"Cyntoia is shocked and surprised that so many celebrities have all of a sudden decided that they needed to speak out on this and she is very appreciative of their interest and their concern and their support," said attorney Charles Bone.

The first celebrity to share an earlier Instagram post calling for Brown's release was the singer Rihanna. The Instagram post may have been inspired by a segment on Brown aired by a Nashville television station, Fox 17 News, earlier in the week.

Other top celebrities who shared posts calling for her release included Kim Kardashian West, Cara Delevingne, LeBron James and Snoop Dogg.

The system has failed. It’s heart breaking 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. I’ve called my attorneys yesterday to see what can be done to fix this. #FreeCyntoiaBrown pic.twitter.com/73y26mLp7u — Kim Kardashian West (@KimKardashian) November 21, 2017

"This is meaningful not to Cyntoia, but to the cause of sex trafficking and sex slavery and juvenile justice," Bone said.

As a teenager, Brown ran away from home to Nashville, where she met a man nicknamed “Kut Throat,” according to her lawyers. The two began living together in hotels, but the man abused Brown, raped her and forced her into prostitution, they said.

On the day she met Allen in 2004, “Kut Throat” had told her to go out to the streets and bring him back money, according to her lawyers.

Allen picked Brown up in a truck and took her to his home, according to court documents. At his home, Allen showed Brown some of his firearms and then the two got in bed together, according to the documents.

At one point Allen reached under his bed and Brown thought he was reaching for a gun, so she pulled a gun from her purse and shot Allen, according to the documents. She then took money and two guns from Allen.

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Prosecutors charged that robbery was the true motive behind the crime, but Bone said it was a case of self-defense.

"When she was in his home, where she had been bought for sex, he showed her a number of weapons that he owned and she thought she was about to be killed in addition to being raped by this man," said Bone.

Brown was tried as an adult and convicted of first-degree murder and aggravated robbery. She was sentenced to life in prison in 2006 and is currently being held in the Tennessee Prison for Women in Nashville. She will be eligible for parole when she is around 67.

Her case inspired a 2011 documentary called "Me Facing Life: The Cyntoia Brown Story." Bone said he found her sentence "shocking" and decided to work for Brown pro bono.

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Bone said he and a team of lawyers have been arguing for Brown to get a new trial and that if she were tried under current Tennessee law "she would most likely today be charged with second-degree murder at the most."

If Brown faced the lesser charge, that "would put her in a situation now where she would be qualified to be considered for parole."

"The difference in 15 years and 51 years is a lifetime for a person like Cyntoia," he said.

Attempts at appealing Brown's case have so far been unsuccessful, but a habeas corpus petition is still pending in federal court.

Brown's biological mother testified that she drank up to a fifth of vodka or whiskey every day while pregnant, Bone said. She was later adopted. Brown was diagnosed with Fetal Alcohol Syndrome disorder in 2012 by a team of experts, according to her lawyers. That team found that Brown had organic brain damage.

Jeffrey Burks, the prosecutor in Brown’s case, told Fox 17 News in Nashville that Brown should not be considered a victim. Burks is currently an assistant district attorney in Georgia.

"There has been a group of people who have wanted to make Ms. Brown a victim and a celebrity since this happened," Burks told Fox 17 News. "She was not 'trafficked' nor was she a 'sex slave.' It's not fair to the victim and his family that the other side of this case is so seldom heard."

A message left with Burks’ office was not immediately returned on Friday.

While in prison, Brown received her G.E.D. and an associate degree from Lipscomb University, which holds courses on site for women at the prison, Bone said.

Bone said he plans to submit an application to Gov. Bill Haslam to consider a commutation of Brown's sentence. He is also working to challenge the law that permits juveniles to be sentenced to a minimum of 51 years if tried in adult court, he said.

Bone said he hoped these efforts, plus renewed interest in her case, could finally lead to progress for Brown.

"We hope that one of these avenues or maybe all of them could happen in a way that would result in some success here," he said. "We're not giving up."