She said it was remarkable "that one ancestor...could be responsible down the family line for lives that have taken such different and varied paths."
The two men are political opposites, disagreeing sharply on the war in Iraq.
The vice-president is an advocate for using force to try to stabilise the country, while Obama wants to withdraw US troops from Iraq.
'Black sheep'
According to her spokeswoman, Obama, an Illinois senator, is a descendant of Mareen Duvall.
The French immigrant married the granddaughter of a Richard Cheney, who arrived in Maryland in the late 1650's from England, said Ginny Justice, a spokeswoman for Lynne Cheney.
Obama often highlights his rich multicultural family heritage on  the campaign trail - his father was from Kenya and his mother from Kansas.
Bill Burton, Obama's spokesman, offered a tongue in cheek response to the news.
"Every family has its black sheep."