Polanski was arrested Saturday in Zurich. The U.S. has been seeking his extradition for having sex with a 13-year-old girl in 1977.
Tate says Polanski did not forcibly have sex with the girl, calling it a "consensual matter."
Sharon Tate was murdered in Los Angeles in 1969 by followers of Charles Manson. She was eight months pregnant.
Debra Tate says it's been a devastating few weeks for her, with her sister's killer, Susan Atkins, dying Sept. 24 and now her late sister's husband jailed.