I guess determining passion depends on whether or not the wife could reasonably foresee the consequences of telling her husband she was raped. Did the guy have a history of violence or a short temper? He can't claim it was "passion" if he was acting on the belief his wife was in imminent danger. But she was indicted on manslaughter charges.
I'm out of my depth here, talking off the top of my head, but I'm going to keep going and rely on you all to pull me back in somewhere.
If she knew her husband had a gun for protection, and could reasonably infer he would use it, and lied to him, I guess that makes him the weapon. But wouldn't that be criminally negligent homicide?
I guess it would depend if passion is defined as acting out of fear.