Complex sentence: When it came to them both being together, Elizabeth murdered Edwin and planned on murdering Agnes, she made Monks kill her, but Agnes ran away, her sister Rose (Keira Knightley) witnessed this and was left traumatized.
Split into simpler sentences: When it came to them both being together, Elizabeth murdered Edwin and planned on murdering Agnes. She made Monks kill her, but Agnes ran away; her sister Rose (Keira Knightley) witnessed this and was left traumatized.