Mollie Tibbetts would have been 21 Tuesday. But the University of Iowa student was slain during a routine evening jog July 18 in her hometown of Brooklyn, Iowa.
Her mother, Laura Calderwood, has grieved in private for 9 months.
But in honor of Mollie's birthday, Calderwood granted her first TV interview since Rivera's arrest.
She told CBS Des Moines affiliate KCCI-TV she has "good days and bad days. I'll have a week of bad and then a week of good, but I just try and find the silver lining in it."
Calderwood said the main thing is that, "We don't want Mollie to ever be forgotten, and we want to continue in her footsteps.
"I want people to remember that Mollie lived life to its fullest, and she wants us all to go on living our best potential life."
"We're trying to make the world a better place in her memory," Calderwood continued.
Calderwood told KCCI she's relieved authorities found Mollie's body. "There was a sense of relief that we knew where she was. Part of my fear is that she would never be found," she recalled.
KCCI says Iowans donated money and spread acts of kindness to mark Mollie's birthday.
Calderwood urged people to donate $21 to the Mollie Tibbetts Memorial Fund, which benefits the University of Iowa Stead Family Children's Hospital's pediatric and adolescent psychiatric unit.
Calderwood said mental health awareness and treatment, especially in young people, will be Mollie's lasting legacy. She was passionate about it, Calderwood emphasized.
"I know that Mollie went through a period of suffering from anxiety, and so I think she knew what it felt like," she said. "I went through that process with her and I call it situational anxiety. I knew what it was. It's not a pleasant thing, and it can manifest itself in all kinds of physical ways."
In Brooklyn, community members gathered Wednesday for a fundraiser in Tibbetts' memory for the restoration of the Brooklyn Opera House.