"I still cannot understand why I did what I did," Melissa Huckaby told the courtroom.
"I want you to know that she did not suffer," said Huckaby.
She was sentenced to life in prison for killing Sandra Cantu.
A court official held a microphone in front of her as she begged forgiveness.
"I can't imagine forgiving someone who would harm my own daughter but I hope that some day you can forgive me," she said.
Huckaby wiped away tears in the darkened courtroom as a slide show documenting Sandra's too-short life was played.
Sandra vanished from her home in Tracy, California, near San Francisco. Surveillance video caught the little girl skipping down the street the day she disappeared.
Soon after her mother made a heartbreaking plea for Sandra's return, her body was found, stuffed into a suitcase and dumped at an irrigation pond near her home.
She was carried to her last resting place in a horse-drawn hearse.
But if Sandra's murder shocked the community, the arrest of 29-year-old Melissa Huckaby, who looked very different back then, sent it reeling.
Huckaby, whose daughter was friends with the dead girl, was initially charged with sexually abusing and murdering Sandra.
The sex abuse charge against Huckaby was dropped as part of a plea deal that also spared her the death sentence. She pleaded guilty to first degree murder.
At the sentencing, Sandra's father Daniel couldn't contain his anger toward Huckaby.
"You took the life of an innocent little girl and she didn't do anything. She wasn't even old enough to decide to eat ice cream yet," said Daniel Cantu.
Sandra's aunt, Angie Chavez, spoke on behalf of the dead girl's mother.
"The pain of knowing that she was so close to home and we couldn't protect her from Miss Huckaby is unimaginable," she told the court.
The killer's mother spoke directly to Sandra's mother.
"From mother to mother, I am so sorry," said Judy Lawless.
Melissa Huckaby also told the court she would live with her to decision to kill a "sweet and innocent" girl for the rest of her life.