Hoshi Sato's speaking voice is the same as Linda Parks (from youtube) she wasn't employing a accent. What we were hearing on the show was Linda Park's normally accented speaking voice. A accent she came by through growing up in San Jose, California
Hoshi Sato possessed an Pacific coast American accent, and most likely was a "American Female."
Hoshi was born in Kyoto. I guess you could explain her accent by saying she was raised in North America, or something.