Wikimedia Commons/Friends TV show TV Reese Witherspoon played Rachel's sister on Friends, but was terrified. Jennifer Aniston reveals how she calmed her nerves. April 26, 2026 AceShowbiz - Friends is famous for featuring numerous A-list guest stars, including Reese Witherspoon, who portrayed Jill Green, the youngest sister of Rachel Green, played by Jennifer Aniston. Witherspoon appeared in two episodes during Season 6: "The One With Rachel's Sister" and "The One Where Chandler Can't Cry.