First of all just keep in mind that intrusive thoughts aren’t a measure of who you are as a person. Everyone gets them. In fact, the more you think about how much you hate them, the more likely you are to get them. So try not to worry too much over them.
Maybe ask your parents if there’s anything you can do about giving you and your sister space apart from each other. You’re teenagers, it’s healthy to have separate rooms. If you can’t afford that, which I’m guessing from your description you can’t, even just putting up a curtain or a partition between your halves of the room might help.