Complex sentence: It is there that she sets a trap to kill Faile and the others so that she may escape, but when Perrin attacks and drives the Shaido away Therava finds her and forces her once again to become "gai'shain".
Split into simpler sentences: It is there that she sets a trap to kill Faile and the others so that she may escape. When Perrin attacks and drives the Shaido away, Therava finds her and forces her once again to become "gai'shain".