Updated 3:04 p.m. ET, 9/1
(CNN) - Mary Cheney, daughter of former Vice President Dick Cheney and sister of Wyoming GOP Senate candidate Liz Cheney, said her sister was "dead wrong" in her statements about same-sex marriage last week.
"For the record, I love my sister, but she is dead wrong on the issue of marriage," Mary Cheney wrote in a private Facebook post Friday night, according to The New York Times.
Mary Cheney married her longtime partner, Heather Poe, last year in Washington, D.C., which legalized same-sex marriage in 2009. The couple have two children together - a son, Samuel, and a daughter, Sarah.
"Freedom means freedom for everyone," Mary Cheney added. "That means that all families - regardless of how they look or how they are made - all families are entitled to the same rights, privileges and protections as every other."
Liz Cheney said last week she is "not pro-gay marriage" and believes the issues of marriage should be left up to voters in their respective states, not to judges or legislators.
The statement, Cheney's campaign said, was in response to reports of a "push poll" in Wyoming that was asking voters if they were aware Cheney "supports abortion and aggressively promotes gay marriage."
"The people of Wyoming deserve an honest campaign," Cheney said. "They should not be subject to the kind of dirty tricks this push poll represents."
Cheney, who chairs a nonprofit on national security and education called Keep America Safe, is challenging Wyoming Republican Sen. Mike Enzi for his seat.
Mary Cheney's sexual orientation was known during her father's first run in 2000 for vice president, though her family generally declined to discuss her personal life on the campaign trail.
Dick Cheney has said in the past that gays and lesbians should be allowed to marry, though like his daughter Liz he says regulations should be handled at the state level.
- CNN's Ashley Killough and Kevin Liptak contributed to this report.