They Called Her the ‘World’s Ugliest Woman.’ It Only Made Her Stronger.

The experience inspired Lizzie Velasquez to appear in a new documentary

Lizzie Velasquez will never forget the day she came upon a YouTube video with 4 million views and thousands of mean comments naming her the “World’s Ugliest Woman.” She was only 17 years old.

“When I saw it my whole world just felt like it crashed at that moment,” Velasquez, 26, tells PEOPLE of the experience that inspired her new documentary A Brave Heart, which premiered on Saturday at SXSW in Austin, Texas. “I thought, how in the world can I ever pick myself up from this?”

But Velasquez – who weighs just 63 lbs. due to a rare syndrome that doesn’t allow her to gain weight – did just that by becoming an anti-bullying activist and motivational speaker.

“If I ever see that person [who made the video] I would jump on them and give them the biggest hug in the world and tell them, ‘Thank you for bringing the best thing that has ever happened to me in my life,’ ” she says. “That video changed everything and it has given me the platform that I have now to be the voice for anyone who’s ever been bullied – and not just myself.”

After giving a TEDx talk that went viral, Velasquez was approached by the group Women Rising and director Sara Bordo, who asked if she could document Velasquez’s daily existence and efforts to lobby for the country’s first federal anti-bullying bill. She also gained the attention of YouTube star iJustine who is an executive producer on the film.