@fake name Does your cat stay indoors all the time?
Cats are born to be free and independent. In my case, every single cat I've had (my current one included) did things like those you described at first. They'd shit under my bed (and sometimes on it too haha) and mess around with everything.
But as time passed, they'd grow up and start going out and come back on their own. And at this point I'd never even see them shit/piss at home again and they'd be way more laid back than before.
I don't know how safe it is to let your cat outdoors where you live but that can be the solution. Let her out at least during daylight. But let's of course take Teloc Vovim's advise and keep 'em in on Halloween. Not only this but also take care of them all the time, specially if they are used to go out and come back on their own.