Mourne Mountain Rescue Team were called at 13:35 GMT after emergency services were unable to locate the woman in Tollymore Forest, near Newcastle.
An Irish coastguard helicopter was called in due to the nature of the woman's injuries and her location.
She was treated for head, neck and back injuries.
More than 20 people from the Northern Ireland Ambulance Service, the police and coastguard and forest service staff assisted in the rescue operation.
Mourne Mountain Rescue Team posted details of the rescue on its Facebook page on Sunday.
Nine-year-old Matthew McArdle from Newry took photos of the rescue operation.
A woman is recovering after she was airlifted to Daisy Hill Hospital, Newry, following a horse riding accident on Sunday.