Carmela Dela Rosa, 50, of Fairfax was arrested and charged Tuesday with murder, said prosecutor Ian Rodway, the chief deputy Commonwealth's attorney.
The child, Angelyn Ogdoc, died in a hospital after plunging to the pavement Monday night. She fell from a walkway linking the mall's third floor to the parking garage's sixth floor at Tysons Corner Center in Fairfax, a Washington suburb in Virginia.
Investigators believe Dela Rosa threw the child over a railing but do not yet know why, Fairfax County police spokeswoman Tawny Wright said. Wright said the toddler and Dela Rosa were leaving the mall with family at the time.
Dela Rosa was being held without bond, and a preliminary hearing in the case was set for Jan. 4, Rodway said. A public defender will be assigned to the case.
One of Dela Rosa's neighbors, Russell Jackson, described them as "a happy family" and said Dela Rosa lived with her husband and a son, but that their daughter and granddaughter were frequently at the home.
Jackson, who lives in a row house directly next door to the family, said the grandparents would often take care of the young girl.
"She was a sweet, happy baby," he said, adding that Dela Rosa and her grandchild could often be seen in the window of the home, waiving to passers-by.
No one answered the door Tuesday at Angelyn's two-story home in Falls Church, about seven miles from the home of the grandparents.
Associated Press Writer Jessica Gresko in Washington contributed to this report.