Zahra was reported missing by her stepmother and father on Oct. 9, but police say no one outside of the family has reported seeing her since Sept. 25.
The girl had a grueling life. Stricken with bone cancer, she lost her left leg and much of her hearing. Relatives and neighbors said Elisa Baker was abusive to Zahra, who was often bruised.
Zahra's birth mother, Emily Dietrich, flew from her home in Wagga Wagga, Australia, last month and visited the Hickory, N.C., house where Zahra had been living with her father and stepmother.
Dietrich had given up custody of her daughter when she was a baby. Zahra later moved with her father to America when he decided to marry Elisa Baker, who he had met on the Internet.
Dietrich, who hadn't seen her daughter since the girl was 8 months old, has since expressed hope that Adam Baker was not involved in her murder.
"I have to take a step back and think of the possibility that maybe Adam [Baker] wasn't involved and maybe he is hurting as well," Emily Dietrich told the Australia-based Seven Network.