KVUE — A YouTube video intended to bully an Austin woman with a rare syndrome motivated her to become an anti-bullying activist. Now she's debuting a documentary about her life at SXSW.

Lizzie Velasquez acts like any other 26-year-old, but there's no denying something about her is different.

"The doctors said they had never seen a child like that and they didn't know exactly what was going on with her," her mother said. Born eight weeks premature, Velasquez has an incredibly rare syndrome that prevents her from gaining weight.

On Sunday Velasquez and her family discussed how her syndrome has launched her into the national spotlight. Not because it is so uncommon, but because of how she is fighting back against cruel attacks.

When she was 17 years old, Velasquez was browsing YouTube looking for music to listen to when she saw a thumbnail that resembled her. She clicked on it to find an eight-second clip of her with no sound titled, "The Ugliest Woman in the World."

"I don't even know why I clicked on it," Velasquez said. "But I did, and that's when I lost it. Calling me a monster or asking me why my parents didn't abort me. 'Kill it with fire. I wish you were dead.' Just pick up a gun and end my life.' It hit me like a ton of bricks. It was completely unexpected. And I cried, of course," Velasquez said.

"She was just so heartbroken. I was just as heartbroken, but I had to tell her that she just had to forgive the person that did that because you have to forgive in order to move on," said her father.

Velasquez took her father's advice and turned her tears into triumph, launching a campaign to educate and end bullying.

In December 2013, she spoke at TEDxAustin Women. "Am I going to let the people who said 'kill it with fire' define me? No," she said to a cheering crowd.

That was the springboard. Months later she started working on a documentary, telling her story and furthering her campaign against bullying. A Brave Heart: The Lizzie Velasquez Story is now premiering at SXSW.

There are two upcoming screenings of the documentary, Monday at 2:30 pm at the Alamo Drafthouse on Slaughter Lane and Thursday at 6:30 pm at ZACH Theater.

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Read the full story and watch the video on KVUE.com.