It appears your mother has a serious medical condition which warrants immediate evaluation by a physician. Her symptoms are concerning for meningitis but are also consistent with the flu.
Sustained fever with abdominal pain, severe headaches, vomiting, and a history of gallstones (suggested by incomplete gall bladder emptying) is especially concerning for cholangitis. Cholangitis is a bacterial infection of common bile duct that drains the bile from the liver into the gall bladder and small intestines. It occurs most commonly from a gallstone obstructing the outflow of bile. Cholangitis is a life threatening condition and warrants immediate medical attention, antibiotics, and removal of the stone.