"I was warned about texting and driving, but I always thought, 'It's not gonna happen to me,' " Liz Marks tells PEOPLE.
In April 2012, just two weeks shy of her 18th birthday, Marks' sedan plowed into the back of a flatbed truck that had stopped to make a left turn. She had been reading a text at the time – just one word sent from her mother: "OK."
Marks was airlifted to the University of Baltimore Shock Trauma Center where she remained in the ICU for one month as she underwent multiple surgeries to reconstruct her face and skull.
"I'm deaf in my left ear, blind in my left eye, I lost the ability to smell and I lost all my short-term memory," Marks, now 21, says. "I lost the ability to fall asleep without medication, I had to relearn how to walk, talk, read, write – everything."
Marks spent three months at a rehab facility relearning how to complete the most basic human functions. During that time, she says she lost all of her friends. "They all moved on," she says. "I developed a new personality and they didnâ€™t like who I became."
Marks' story made national headlines and the U.S. Department of Transportation created a video about her experience that has been viewed more than 9 million times. Now, Marks and her mother, Betty Shaw, will appear on an episode of Oprah: Where Are They Now? to share how the near-fatal accident has given both women purpose.
"It happened for a reason," Marks says of the accident. "I'm able to change people's minds about texting and driving because once I tell my story, people know it's not worth it and they stop."
Unable to go to college due to her injuries, Marks has dedicated herself to public speaking to raise awareness about the dangers of distracted driving.
"I know I'm making a big difference around the world and I'm very happy," she reflects. "It makes me feel stronger."
Her work has also given Shaw – who sent the text Marks was reading at the time of the accident – to heal alongside her daughter.
Marks and Shaw's episode of Oprah: Where Are They Now airs Saturday at 10 p.m. ET on OWN. Learn more about Marks's campaign against distracted driving on Facebook and download the app she inspired to curb texting and driving.
"When Liz decided to share her story, I was weary because I didnâ€™t tell anyone that it was my text that caused her accident and I was devastated, I was embarrassed, I was ashamed," Shaw tells PEOPLE. "But I thought, 'If she's willing and brave and strong enough to share her mistake, then I need to step to the plate and stand beside her.' "