Rose Friedman, a free-market economist whose extraordinary collaboration with her husband, Milton, proved essential to his Nobel-prize-winning career, died Tuesday at her home in Davis, Calif. Her birth records have been lost, but her family said she was probably 98.

The cause was heart failure, according to a statement approved by the family and issued by the Friedman Foundation for Educational Choice, founded by Milton and Rose Friedman in 1996 to promote school vouchers and other school-choice policies.

Rose Director, as she was known after her family emigrated to the United States from Russia, met Milton Friedman in 1932 when they were both graduate students at the University of Chicago. They wed six years later, and their marriage lasted 68 years, until Mr. Friedman’s death in 2006.

A Nobel laureate and a giant of 20th-century economics, Mr. Friedman was a libertarian thinker who believed that government had an obligation to clear a path for markets and that economic freedom was crucial to a free society. His work provided a fundamental stanchion of the presidency of Ronald Reagan and the administration of Margaret Thatcher in Britain.