Bush had an independent streak and could be sharp-tongued. As first lady, she promoted literacy and reading but said she was more interested in running a household than helping her husband run the country.

She discouraged speculation that she wielded political influence with the president like her predecessors - Ronald Reagan's wife, Nancy Reagan, and Jimmy Carter's wife, Rosalynn Carter.

"I don't fool around with his office and he doesn't fool around with my household," she once said.

"She'll speak her mind but only to him," said Jack Steel, a longtime Bush aide.

The only other woman to be both wife and mother of US presidents was Abigail Adams, the first lady from 1797 to 1801. She was a major influence on husband John Adams, the nation's second president, but died before son John Quincy Adams was elected president in 1824.

Another of Bush's sons, Jeb, who served as governor of Florida from 1999 to 2007, sought the 2016 Republican presidential nomination and she campaigned for him before he dropped out of the race.