Sarah Michelle Gellar is an actress who voiced the inquisitor Seventh Sister in several episodes of Star Wars Rebels. Her most famous non-Star Wars role is Buffy Summers from the classic TV series Buffy the Vampire Slayer.
Gellar has won several awards in her career including a Daytime Emmy Award for All My Children and several Teen Choice Awards for her roles in Buffy the Vampire Slayer and the film Scooby-Doo (where she played Daphne). Gellar is married to Freddie Prinze Jr. who voices Kanan in Star Wars Rebels.
Here is Gellar talking about Seventh Sister at New York Comic-Con. She also talks about other strong female characters in Star Wars in this clip.