She remembers being told by someone: "God must have a plan for your life."
"I realized God existed, and He had a plan, but at the time I didn't know who God was. And at the time, people were questioning how could God allow something like this to happen," Mary Gianna said.
Every day, the next school year, she would walk by the spot where the library used to be – since so many of the killings took place there, it was demolished and eventually rebuilt in a different spot – wondering why she had been spared. At that time, she had the stirrings of faith, but still no clear answers.
She said she started drinking, going to parties, looking for other things to offer fulfillment – but she knew in her heart it wasn't where she was supposed to be. Her senior year, she said, she felt like she had finally reached "rock-bottom" and lost all hope.
"It was in those moments that I felt like I just couldn't go on in life that one of my friends invited me to the Catholic Church at St. Francis Cabrini in Littleton, Colorado," she said.
Immediately upon walking in, she met a representative of Franciscan University of Steubenville in Ohio, who encouraged her to consider going there for college. She also met a youth minister named Kate.
"She started telling me about a God that passionately loved me," Mary Gianna recalled.
Kate started taking her out for coffee and telling her about God's love – that He does have a plan, that Mary Gianna was made in his image and likeness. Growing up, she had no direction in life, Mary Gianna said, and God's love was that thing that she had been missing.
"Not only did God lead me out of Columbine that day – he was leading me home on that day. He was leading me to Himself," Mary Gianna said.
"And I wanted to say 'yes' with all my heart to God's plan. I realized that He had a plan, and I wanted to say 'yes' to that plan."
She ended up enrolling at Franciscan University, even though at first her father had misgivings about the cost. Later on, however, it seemed his heart had been changed. Mary Gianna said her parents were very supportive of her faith and the direction her life took after her conversion.
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She went through RCIA her freshman year at Franciscan, and at the Easter vigil Mass on March 30, 2002 at the age of 19, she was received into the Catholic Church.
Mary Gianna experienced the call to religious life in 2008, when she went to the Cathedral of St. Paul in St. Paul, Minnesota and prayed that she would be able to enter into the Mass in a way she had never experienced before.
It was through Mass that she felt God's presence before her. She walked out of the chapel changed; all she wanted was religious life.
She chose a charismatic, Franciscan, contemplative, and missionary order called the Disciples of the Lord Jesus Christ, which brought her to Prayer Town, Texas, northwest of Amarillo. She pronounced her final vows on August 4, 2018.
Twenty years on from the Columbine tragedy, Mary Gianna said she thinks more of her former classmates are finding the strength to talk about what happened that day. She said she keeps in touch with some of her classmates, teachers, and the former principal of the school, especially her friend who left the school with her that day. They've talked about the experience since.
"I often think of the greatest tragedy of Jesus being put to death on the cross, and how it led to our salvation, and that even in the midst of the tragedy at Columbine, God can bring good," she reflected.