Hell she got off easy. I've been known to put my brothers into the ground for interrupting my gaming session.
Because she's type who can't close her mouth whenever she does, making her fallen asleep is best decision. Who'll know what she'll say in public when you do something to her and she's conscious.
This reminds of an ero manga I read a year or two back but I can't remember the title or artist name for it.
Guy tries slipping his sister a sleeping pill in her drink which she spots immediately but pretends she took it anyway thinking she could catch him in the act of trying things with her body. Only for him to start fapping to porn dvd thinking she wasn't listening to him.
They did do the deed together eventually but I can't remember how it played out completely.