Complex sentence: Her identity is a mystery until the end, when the audience sees Ellen's flashback to Herod lynching her father, a sheriff, and giving her a chance to save her father by shooting the rope and severing it, but it goes wrong.
Split into simpler sentences: Her identity is a mystery until the end, when the audience sees Ellen's flashback to Herod lynching her father, a sheriff. Herod gives Ellen a chance to save her father by shooting and thereby severing a rope, but it goes wrong.