Have you tried Feliway? I know I sound like a broken record but so many people here swear by that and Rescue Remedy. These are supposed to help calm the kitties and ease the aggression issues. I'm sure those that use it will be able to tell you a lot more about it.

I would really try one of those before you start trying to rehome Strauss. Hopefully something as simple as this may help remedy the situation. It certainly sounds pretty intense if Sid is missing a piece of her ear!!

Good luck and keep us posted.