New Jersey authorities issued McMath another death certificate, dated June 22.
Winkfield has filed two lawsuits in California, which seek to invalidate the state's death certificate.
Winkfield's attorney, Chris Dolan, said the New Jersey death certificate should strengthen Winkfield's legal position.
She is suing the doctors and Oakland's Children's Hospital for medical malpractice, alleging surgeons botched what should have been a routine tonsillectomy.
Damages in California for so-called non-economic harm in medical malpractice cases for pain and suffering and the like are capped at US$250,000 when the patient dies.
The hospital and Winkfield were wrangling over that in court when New Jersey issued its death certificate. Dolan said it's unclear how the new death certificate will affect the medical malpractice case.
Dolan has also filed a federal civil rights lawsuit, which seeks to invalidate California's death certificate.
At the funeral service Winkfield said she kept up her fight because of her deep Christian belief her daughter was alive and could respond to her name and simple commands to wiggle a finger or toe.
She criticised the doctors who insisted her daughter was dead and said she was fighting to eliminate "brain death" as a diagnosis.
"Stop letting them pull the plug on your people," Winkfield said of doctors. "They are not God."
New Jersey's Medicaid programme, donations and family members paid for the girl's care. Winkfield said she sold her California home and drained her savings to keep her daughter on life support.
During the service, she was lauded for her determination and strength. Jahi's body was taken to nearby Hayward for burial.
- AP