DENVER (AP) — Anne Marie Hochhalter, who was partially paralyzed in the Columbine High School shooting but found strength to forgive and to heal her soul after bonding with another family devastated by the tragedy, has died. She was 43.

Hochhalter was found in her home in suburban Denver on Sunday. Her family suspects she died of natural causes stemming from her injuries in the 1999 shooting in which 12 students and a teacher were killed.

The investigation into how she died has been transferred to the office that conducted the autopsies of those killed at Columbine, the coroner's office for Adams and Broomfield counties said.

Hochhalter in 2016 wrote a letter to one of the gunmen’s mothers saying, “Bitterness is like swallowing a poison pill,” and offering her forgiveness. Attending a vigil on the tragedy’s 25th anniversary last year — after skipping a similar event five years earlier — she said she was flooded with happy memories from her childhood and wanted those killed remembered for how they lived, not how they died.

Hochhalter struggled with intense pain from her gunshot wounds over the past 25 years. Yet her brother said she was tireless in her drive to help others — from people with disabilities to rescue dogs and members of her family.

“She was helpful to a great many people. She was really a good human being and sister,” her brother, Nathan Hochhalter, said Tuesday.

Her own tragedy was compounded six months after the shooting, when her mother, Carla Hochhalter, went into a pawnshop, and asked to look at a gun before using it on herself.

In the wake of her mother’s death, Anne Marie Hochhalter was embraced by another family who lost a daughter at Columbine.

Sue Townsend, whose stepdaughter, Lauren Townsend, was killed, reached out to help Hochhalter as a means of easing her own pain. At first, Townsend took Hochhalter to doctor’s appointments and physical therapy, but their bond soon deepened as they got lunch and went shopping together and eventually began sharing family dinners and vacations.

Townsend and her husband, Rick, called Hochhalter their “acquired daughter."

On a trip to Hawaii together, Hochhalter, who used a wheelchair, was able to float in a lagoon pain-free, she said.

“This relationship would never had happened if it hadn’t been for Columbine. So I tried to focus on the gift that Columbine gave us in Anne Marie instead of what it took away,” Townsend said.

In 2016, the mother of one of the Columbine gunmen, Sue Klebold, released a memoir exploring the causes of her son's violence and ways to prevent future attacks through mental health awareness. Hochhalter said at the time she was grateful that Klebold was donating the book proceeds to help those with mental illness. Hochhalter said her mother suffered from depression and did not believe the shootings were directly to blame for her death.

She said she was sure Klebold had agonized over what she could have done differently just as she had thought of ways she could have prevented the death of the mother she loved.

"A good friend once told me, 'Bitterness is like swallowing a poison pill and expecting the other person to die.' It only harms yourself. I have forgiven you and only wish you the best," Hochhalter said in a message she posted on Facebook. She also included a photo of a card Sue and Tom Klebold sent to her as she recovered in the hospital after the shooting.

Hochhalter attended the 25th anniversary vigil in April with her brother, who was trapped in a classroom during the shooting. She had not attended the 20th anniversary event because of post-traumatic stress disorder, she said in a social media post last year.

“I’ve truly been able to heal my soul since that awful day in 1999,” she wrote.