(CNN)For Natalie Reilly, Valentine's Day 2016 was grim. The divorcee was at home nursing her mother through a 19th round of chemotherapy.
"She was not eating, and she was not coming out of her room," Reilly remembered of her once-vibrant mom. "It was really hard for me -- she was the strongest woman I knew."
In the midst of feeling sad and sorry for herself, Reilly drew inspiration from her mother's strength. A new idea dawned.
"I thought to myself: 'This is not who she raised me to be,'" she told CNN. "I said, 'We are not going to feel sorry for ourselves. We are going to do something for our community.'"
Mother and daughter spent the next three hours writing "thank you" cards and handing them out to veterans and first responders.
Their first note went to a Korean War vet at a grocery store. He was deeply touched by their kindness.
By the time they were done, her mother was laughing and smiling. The notes became their ongoing project.
As their mission touched more people, her mom's health continued to decline, eventually requiring hospice care.
A deathbed promise
On her deathbed, Reilly's mother asked her to keep spreading love through the notes. She also had another message for her daughter.
"Mom said, ' When God takes something, he usually gives you something in return and it's something bigger and better.'"
Two years ago, Reilly's mother died. The dutiful daughter continued writing notes each day.
"The night my mom died, when she started to slip away, I felt like I had something to run to," she said.
She feels her mother's presence in each and every letter.