Amy Yu was located in Mexico on Saturday night, ABC News confirmed after speaking with Yu's mom.
"I'm really happy. Please let everyone know," she told ABC News.
Just a day ago, Luu made a public plea to her daughter to come return to her in an interview with ABC News.
"Amy, I love you. Can you come back?" Miu Luu of Allentown, Pennsylvania, said Friday.
Yu, along with Kevin Esterly, 45, had been missing since March 5, and when the girl did not return home from school that night, her mother reported her missing, the Allentown Police Department said.
Amy was believed to have willingly accompanied Esterly out of the country on a one-way flight by way of Dallas, Texas.
Authorities said he withdrew $4,000 from his wife's bank account and signed the youth out of the school, claiming to be her stepfather.
Esterly is facing a felony charge of custodial interference.
Authorities say Yu has been safely returned to the U.S.