“Take your anger and… just spread happiness and love and memory for my lovely niece,” Ms Chernykh said.
“I hope maybe she’s an angel now. Maybe she [will] send some good vibes to the world.”
Jewish community leaders have in recent days suggested the tragedy was an inevitable result of Australia struggling to address rising antisemitism.
The attack on Sunday, which targeted the Jewish community at an event celebrating the first night of Hanukkah, was the country’s deadliest incident since 1996, when a gunman killed 35 people during the Port Arthur massacre.
Ahead of Matilda’s funeral on Thursday, Ms Chernykh said the family was devastated.
“I look at their faces [and] I don’t know if they will be ever happy again,” she said of Matilda’s parents.
Matilda’s younger sister, from whom she was “inseparable”, is shattered and confused, she said.
“She doesn’t have enough tears to cry.”
At a flower memorial on Tuesday, Matilda’s mother Valentyna told mourners that the family came to Australia from Ukraine more than a decade ago, thinking it would be a safe place for them.
“I couldn’t imagine I’d lose my daughter here… It’s just a nightmare,” she said.