Marcial Garcia Hernandez, 45, and Inez Martinez Garcia, 43, were arrested Thursday on suspicion of 13 felony counts of aggravated sexual assault of a child under age 14.
San Diego County Sheriff's Department officials said the girl, whose name was not reported, was smuggled into the United States when she was 12, and the alleged abuse occurred over a 21-month period.
The couple forced her to care for their three children and have sex with Hernandez, and beat her when she refused, said Deputy G. Crysler, an investigator with the North County Human Trafficking Task Force.
The girl was forced to lie about her age to work in a local restaurant and to have sex with older men as a prostitute, Garcia and Hernandez keeping her income, arrest documents said.
Authorities were called in after Hernandez allegedly beat the girl.
The alleged victim returned to Mexico but came back to the United States to assist in the criminal investigation, the Los Angeles Times reported.