Justin Anthony, the girl's cousin, said she had no pre-existing conditions and hadn't recently travelled to any foreign country, according to The Daily Mail.
Anthony said that as of Saturday, she is in stable condition at the Children's Healthcare of Atlanta-Scottish Rite Hospital.
The family does not know how she contracted the virus, according to Anthony.
Mr Anthony said she was placed on a ventilator at Children's Healthcare of Atlanta-Scottish Rite Hospital. "Additional details will not be released due to patient privacy laws", said hospital spokeswoman Jessica Pope.
Children can contract and spread the virus, but their symptoms are generally milder.
At least 195 people have tested positive for the coronavirus in SC. and three people have died, according to public health officials.
The patient was the first confirmed case of COVID-19 in the central San Joaquin Valley.
Young adults have better outcomes than the elderly, but they too are not immune to the virus.
In the United States alone, the novel coronavirus has infected 35,060 people and has killed 457 deaths.
'I know first hand how unsafe it is, ' Anthony said.
'But here's a 12-year-old fighting for her life.
In England, 37 more people who tested positive for COVID-19 have died.
In an email to judges and department heads in the county courthouse, 5th Circuit Solicitor Byron Gipson said the person "was in the building during the week of March 9, 2020, and was last in the building on March 16".
There were no ICU admissions reported for those under age 19, the report said. People need to take care of their children.
According to the state's latest figures on the CCP virus, about 1 percent of cases in Georgia are between the ages of 0 and 17, reported the Atlanta Journal-Constitution.
This article was reproduced from CNN with permission.