The girl, Mia Gonzalez, was found unresponsive inside a car with her mother on Thursday. Investigators believe she strangled her own child.
Candles and flowers are now being placed at a memorial for Mia at the family's home.
Mia's godmother, Noemi Lopez, says she doesn't understand how this could happen.
"Mia was a really good kid," Lopez told Eyewitness News. "She was the light of my home. She didn't deserve this."
Mother arrested for murder after 4-year-old daughter found dead in East Los Angeles
On Thursday night the East LA sheriff's station received a call of a child assault on Civic Center Way. Deputies found Mia and her mother in a car. The coroner says Mia was strangled.
Her mother, 38-year-old Maria Avalos, was arrested for murder.
Mia's father, speaking in Spanish, says there were problems with Avalos but he never thought something like this could happen. Family members say Avalos left with her daughter in the car early last week.
"We were trying to contact her," Lopez said. "She wasn't responding for two days. She said she needed space, that she was going through a lot."
The family says investigators told them the mother might have been driving around with the deceased child for several days before they found her.
"She should've asked for help," Lopez said. "She should've called me. Now she's trying to call me from jail. What does she want now? She already did her part, now let me do my part."
The family has set up a GoFundMe to help with funeral expenses.
Investigators say the case will be presented to the District Attorney's Office for review on Tuesday.