Saki's a pretty cool show. I learned the basics of mahjong thanks to it (and various h-games based off of Saki, To-Love-Ru, Princess Brave, etc. >_>). But yeah, the characters are a big draw. Nodoka and Yuuki, for example.
The character in question is Satomi Kanbara, the lieutenant (third-in-line) and third year from the high school, Tsuruga Academy. Said school is an unknown school that miraculously made it into the finals, but is considered the underdog (because they are new, have not been prominently shown, and aren't the main characters, lol). The next episode, episode 11, will have her face off against the first-year Seika Bundou from Kazekoshi, second-year Hajime Kunihiro from Ryuumonbochi, and third-year (main character, lol) Hisa Takei from Kiyosumi.
Though the resemblance to Rin is there, I had her pegged for Heart Aino from Arcana Heart. Hair's not as pink or hearty, though.