Officials said the woman from Long Beach fell off a walkway around 8:30 p.m. and plunged into the water below.
"The woman and her boyfriend had been leaving the ship walking along a walkway. It was during that time that she climbed up on the railing and fell over into the water," said Nancy Pratt of the Long Beach Police Department.
The woman's 40-year-old boyfriend dove into the frigid waters to try and save her.
The woman was rushed to St. Mary Medical Center, where she was pronounced dead.
The victim's boyfriend was taken to the hospital to be treated for hypothermia.
Two Long Beach police officers also jumped into the water, but they were not hurt. A ship employee also dove in to help.
The circumstances of her fall are not known, but according to Long Beach police and firefighters, the woman had been drinking.
The victim's name has not been released.
"We send our sincere condolences to the woman's family regarding this very sad tragedy," said Greg Keebler, Queen Mary's task force general manager, in a statement. He added that they are working with local investigators.
Long Beach police said the incident was being investigated as an accident, not a crime.