Mary Cheney, the daughter of former vice president Dick Cheney, has responded to her sister Liz Cheney's assertion that she does not supporter her marriage to another woman.

During an appearance on Fox News Sunday, Liz Cheney, who is challenging Wyoming Senator Mike Enzi in the upcoming Republican primary, said that while she loves her sister, she does not support gay marriage.

(Related: Liz Cheney loves her sister Mary but disagrees on gay marriage.)

“Listen, I love Mary very much. I love her family very much. This is just an issue on which we disagree,” she said.

Mary Cheney's wife Heather Poe responded on Facebook: “I was watching my sister-in-law on Fox News Sunday (yes Liz, in fifteen states and the District of Columbia you are my sister-in-law) and was very disappointed to hear her say 'I do believe in the traditional definition of marriage.' Liz has been a guest in our home, has spent time and shared holidays with our children, and when Mary and I got married in 2012 – she didn't hesitate to tell us how happy she was for us. To have her now say she doesn't support our right to marry is offensive to say the least. I can't help but wonder how Liz would feel if as she moved from state to state, she discovered that her family was protected in one but not the other. I always thought freedom meant freedom for EVERYONE.”

Mary Cheney added: “Couldn't have said it better myself. Liz – this isn't just an issue on which we disagree – you're just wrong – and on the wrong side of history.”