Originally Published: 18 NOV 22 07:27 ET

Updated: 18 NOV 22 12:12 ET

By Dr. Tara Narula, CNN Medical Correspondent

Watch "Gabby Giffords Won't Back Down" at 9 p.m. ET/PT November 20 on CNN.

(CNN) -- Doctors and public health experts often talk about a bullet as the vector, just as a virus is the vector of transmission in infectious diseases. Both leave a path of destruction as they travel. Families are left to bury loved ones, and survivors may live with chronic injuries that reveal the damage even one bullet can do.

But some survivors are able to lift their voices for change to keep others from suffering and to shine a light that guides others out of the darkness.

One of those voices that has spoken up in her own unique way is Gabby Giffords. In 2011, the trajectory of a 9-millimeter bullet through the left side of the brain changed the course of her life. The former congresswoman was one of 13 people wounded in a shooting in an Arizona supermarket parking lot. Six people were killed.

It's clear now that she is resilience personified. One step at a time, one word at a time and one day at a time, Gabby has fought to persevere, and her fortitude in the face of tragedy is nothing short of remarkable. She has always seemed to defy the odds, and she does it with grace and her characteristic gentle smile. She has emerged as a leading advocate for gun safety through her own organization, Giffords. But she is also raising awareness around aphasia, a disorder that results from damage to the parts of the brain responsible for language production or processing.

I met Gabby before the debut of the CNN documentary "Gabby Giffords Won't Back Down," a detailed portrayal of the inner fire that helped her heal and pushes her to help others do the same. The day we met, she gave me a big hug outside the small room where I would observe her and four others during their speech therapy session with Dr. Fabiane Hirsch Kruse -- Fabi, as they call her.

Inside the therapy room, Gabby sat around a circular table with Christina, Brian, Matt and Andy, each of them working on exercises designed to help with their aphasia. Fabi asked them to share when they first had their brain injury, how physically active they are and a series of other questions designed to improve their language skills. Often, the answers were single words or the wrong words, or they took several minutes. Sometimes, the answers did not come at all.

Aphasia can be isolating and often misinterpreted. Friends of Aphasia -- the nonprofit founded by Gabby and Fabi -- teaches that loss of words does not mean loss of intelligence.

"It's just because of the injury to the brain," Fabi told me. "It has nothing to do with their ability to think through their thoughts, know who they are, be the wonderful people they are."

Gabby said she loves to talk; she just can't get the words out.

"I'm Gabby," she said, her voice bright and energetic. "I'm so quiet now."

But while the therapy room could have been filled with frustration, instead I saw a room filled with vulnerability, humor and camaraderie. When asked her favorite thing about coming to the aphasia group, one member, Christina, said "hope, hope, hope."

As Gabby put it in the documentary, "Words once came easily. Today, I struggle to speak, but I've not lost my voice."

'Keep moving forward, no matter what'

Therapy for aphasia is tailored to the individual, and recovery can look different for everyone. But one hallmark of treatment is work with a speech therapist; Gabby and Fabi have worked together since 2013.

For Gabby, therapy is "a lot of homework." She is always asking for more. Gabby and Fabi are working hard on perfecting Gabby's ability to deliver more public speeches and interviews.

Part of what has kept Gabby going has also been music. It has been an integral part of her life since her youth, when she was singing in musicals and playing the French horn, and now it's an important part of her therapy. For people with aphasia, anything practiced -- a prayer, a poem or a song -- can be an accessible way to express themselves.

I asked Gabby whether she had a favorite song, and within seconds she belted, loud and clear, the verses of one of my favorite songs.

"Almost heaven, West Virginia ... country roads, take me home to the place I belong," she sang while Fabi danced along to "Take Me Home, Country Roads."

As a cardiologist, I see many patients who have traumatic, life-changing events like heart attack or stroke, and I often urge them not to look too far ahead. Instead, take one small step at a time and find their way back to themselves and to a sense of peace.

What people don't realize, Fabi said, is that Gabby is a daredevil and absolutely fearless. Moving forward is the only way she knows -- before on horseback, motorcycle and bicycle, and now on a trike. She has what Fabi describes as a "beautiful relationship" with her best friend and husband, Sen. Mark Kelly, who has been by her side supporting her each day. She doesn't let anything get her down, Fabi said, and they laugh in every session.

"For me, it has been really important to move ahead, to not look back," Gabby told me. "I hope others are inspired to keep moving forward, no matter what."

In the film, one of Gabby's colleagues says many who meet her are "Gabbified," and now I understand exactly what that means. She has a sparkle and warmth that radiate from somewhere deep inside and a sense of calm and playfulness in her demeanor.

During our interview, when the cameras were about to start rolling, she leaned over and fixed my hair, and it was apparent that she is a natural caretaker. Her compassion comes through in her eyes, which speak much of what her voice at times cannot.

Gabby told me she feels optimistic, but she knows that she has a long road ahead. For the documentary, they'd asked how long Gabby thought she and Fabi would work together. Gabby told them "rocking chairs": a phrase to mean a long time from now, when they're sitting on the porch in old, worn rocking chairs.

At the end of our interview, Gabby and I took a brief walk outside her home. As she held my hand, I could feel both her fragility and her strength. The road for Gabby Giffords has not been easy, but she has not backed down as she continues advancing her own recovery and advocating around both gun violence and aphasia awareness.

I asked, is her fight about reclaiming the old Gabby or discovering a new one?

Gabby answered that it's about the new one -- "better, stronger, tougher."

She walks tall, proud and determined to get the most out of life, both superhuman and down-to-earth at the same time.