Complex sentence: When she refuses to accomplish a mission, the Waif is ordered to kill Arya, but is killed instead while, asserting her identity as a Stark, finally Arya returns to Westeros.
Split into simpler sentences: When she refuses to accomplish a mission, the Waif is ordered to kill Arya, but is killed instead. Arya asserting her identity as a Stark, finally returns to Westeros.