I know what Jo tried to convey, and I do respect your interpretation. But it just didn't work for me in the same manner. Prior to DH Jo did a great job "previewing" characters and elements that would later come into play. Charity Burbage was a jarring one scene presence to me --- I had nothing invested in her and I didn't know what sort of person she was (sinner, saint, whatever). So, the emotion of her murder and Snape's stoic presence was muted for me. It would/should have played like you describe above if only we knew her.