Former Republican Sen. Nancy Kassebaum Baker of Kansas, the first woman elected to the U.S. Senate without previously having a husband serve in Congress, died Friday at 94.

Her son, Bill Kassebaum, told The Associated Press that she died of natural causes.

"She loved Kansas. She loved people from Kansas and representing Kansas for 18 years in the U.S. Senate," he told AP. "She was an independent-minded Republican who was willing to stand up for what she thought was right, even if that meant going against the party."

Kassebaum Baker won election to the Senate in 1978 and served three terms before leaving office in 1997. The daughter of former Kansas Gov. Alf Landon, the Republican Party's unsuccessful 1936 presidential nominee, she built a reputation as a moderate Republican willing to break with her party.

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Her election brought immediate national attention. By the time she announced her retirement, she was one of eight women serving in the Senate and the only woman chairing a Senate committee.

Kassebaum Baker also developed a reputation for working across party lines. A landmark 1996 health insurance law bore her name alongside that of Democratic Massachusetts Sen. Ted Kennedy.

Her political independence occasionally put her at odds with conservatives. She supported an assault weapons ban backed by then-President Bill Clinton and said the vote generated the angriest mail of her Senate career.

Kassebaum Baker remained highly popular in Kansas, winning re-election with 76% of the vote in 1984 and 74% in 1990.

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She married former Republican Sen. Howard Baker of Tennessee in 1996, shortly before leaving the Senate. It marked the first marriage between a man and woman who had both served in the Senate.

Howard Baker, who served as President Ronald Reagan's chief of staff and later as U.S. ambassador to Japan under President George W. Bush, died in 2014.

Kassebaum Baker continued public service after leaving Congress, including serving on a bipartisan commission on campaign finance reform during the Clinton administration.

Later in life, she increasingly broke with the Republican Party's direction and endorsed Democrats in several Kansas races, including Democratic Gov. Laura Kelly.

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She also called for President Donald Trump's impeachment following the Jan. 6, 2021, attack on the U.S. Capitol.

"This just has gone too far," she told Kansas City's KMBC at the time.

Despite her decades in national politics, Kassebaum Baker maintained a close identification with Kansas.

Before leaving for Japan during her husband's ambassadorship, she reflected on what she would miss.

"All I can say is, I will miss the Kansas prairie," she said.

The Associated Press contributed to this report.