Sheena Fujibayashi has one of the funniest character introductions in the Tales series, but right now Lloyd and Collette pity the "Clumsy Assassin." As an ally, Sheena attacks enemies with seals and spirit summons. She attacks Zelos by constantly rejecting his advances.
This video from the Gamecube version shows the party meeting Sheena in English.
Tales of Symphonia Chronicles for PlayStation 3 comes out in Japan on October 10 and is slated for release next year in the West.