I'm getting really aggravated reading this thread.
For those of you bitching at Shrimp because of this, grow the fuck up. He told her not to bring it...it was abundantly clear that the cat was not welcome there. And there's no room for debate on that either: HIS property, HIS rules, no exceptions. Yet she brought it anyways, so it was relegated to a less than ideal environment and it got fukked up. That's on his sister, not him...not one damn bit.
Shrimp, your sister really needs to avoid having any pets anytime soon, because someone who can't even take care of themselves has no business trying to take care of an animal. Sit her down, and really drill this point into her head.